string.c

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/**********************************************************************

  string.c -

  $Author: usa $
  created at: Mon Aug  9 17:12:58 JST 1993

  Copyright (C) 1993-2007 Yukihiro Matsumoto
  Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
  Copyright (C) 2000  Information-technology Promotion Agency, Japan

**********************************************************************/

#include "ruby/ruby.h"
#include "ruby/re.h"
#include "ruby/encoding.h"
#include "vm_core.h"
#include "internal.h"
#include "probes.h"
#include <assert.h>

#define BEG(no) (regs->beg[(no)])
#define END(no) (regs->end[(no)])

#include <math.h>
#include <ctype.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#define STRING_ENUMERATORS_WANTARRAY 0 /* next major */

#undef rb_str_new_cstr
#undef rb_tainted_str_new_cstr
#undef rb_usascii_str_new_cstr
#undef rb_enc_str_new_cstr
#undef rb_external_str_new_cstr
#undef rb_locale_str_new_cstr
#undef rb_str_dup_frozen
#undef rb_str_buf_new_cstr
#undef rb_str_buf_cat2
#undef rb_str_cat2

static VALUE rb_str_clear(VALUE str);

VALUE rb_cString;
VALUE rb_cSymbol;

#define RUBY_MAX_CHAR_LEN 16
#define STR_TMPLOCK FL_USER7
#define STR_UNSET_NOCAPA(s) do {\
    if (FL_TEST((s),STR_NOEMBED)) FL_UNSET((s),(ELTS_SHARED|STR_ASSOC));\
} while (0)

#define STR_SET_NOEMBED(str) do {\
    FL_SET((str), STR_NOEMBED);\
    STR_SET_EMBED_LEN((str), 0);\
} while (0)
#define STR_SET_EMBED(str) FL_UNSET((str), STR_NOEMBED)
#define STR_SET_EMBED_LEN(str, n) do { \
    long tmp_n = (n);\
    RBASIC(str)->flags &= ~RSTRING_EMBED_LEN_MASK;\
    RBASIC(str)->flags |= (tmp_n) << RSTRING_EMBED_LEN_SHIFT;\
} while (0)

#define STR_SET_LEN(str, n) do { \
    if (STR_EMBED_P(str)) {\
        STR_SET_EMBED_LEN((str), (n));\
    }\
    else {\
        RSTRING(str)->as.heap.len = (n);\
    }\
} while (0)

#define STR_DEC_LEN(str) do {\
    if (STR_EMBED_P(str)) {\
        long n = RSTRING_LEN(str);\
        n--;\
        STR_SET_EMBED_LEN((str), n);\
    }\
    else {\
        RSTRING(str)->as.heap.len--;\
    }\
} while (0)

#define TERM_LEN(str) rb_enc_mbminlen(rb_enc_get(str))
#define TERM_FILL(ptr, termlen) do {\
    char *const term_fill_ptr = (ptr);\
    const int term_fill_len = (termlen);\
    *term_fill_ptr = '\0';\
    if (UNLIKELY(term_fill_len > 1))\
        memset(term_fill_ptr, 0, term_fill_len);\
} while (0)

#define RESIZE_CAPA(str,capacity) do {\
    const int termlen = TERM_LEN(str);\
    if (STR_EMBED_P(str)) {\
        if ((capacity) > RSTRING_EMBED_LEN_MAX) {\
            char *const tmp = ALLOC_N(char, (capacity)+termlen);\
            const long tlen = RSTRING_LEN(str);\
            memcpy(tmp, RSTRING_PTR(str), tlen);\
            RSTRING(str)->as.heap.ptr = tmp;\
            RSTRING(str)->as.heap.len = tlen;\
            STR_SET_NOEMBED(str);\
            RSTRING(str)->as.heap.aux.capa = (capacity);\
        }\
    }\
    else {\
        REALLOC_N(RSTRING(str)->as.heap.ptr, char, (capacity)+termlen);\
        if (!STR_NOCAPA_P(str))\
            RSTRING(str)->as.heap.aux.capa = (capacity);\
    }\
} while (0)

#define STR_SET_SHARED(str, shared_str) do { \
    RB_OBJ_WRITE((str), &RSTRING(str)->as.heap.aux.shared, (shared_str)); \
    FL_SET((str), ELTS_SHARED); \
} while (0)

#define STR_HEAP_PTR(str)  (RSTRING(str)->as.heap.ptr)
#define STR_HEAP_SIZE(str) (RSTRING(str)->as.heap.aux.capa + TERM_LEN(str))

#define STR_ENC_GET(str) get_encoding(str)

rb_encoding *rb_enc_get_from_index(int index);

static rb_encoding *
get_actual_encoding(const int encidx, VALUE str)
{
    const unsigned char *q;

    switch (encidx) {
      case ENCINDEX_UTF_16:
        if (RSTRING_LEN(str) < 2) break;
        q = (const unsigned char *)RSTRING_PTR(str);
        if (q[0] == 0xFE && q[1] == 0xFF) {
            return rb_enc_get_from_index(ENCINDEX_UTF_16BE);
        }
        if (q[0] == 0xFF && q[1] == 0xFE) {
            return rb_enc_get_from_index(ENCINDEX_UTF_16LE);
        }
        return rb_ascii8bit_encoding();
      case ENCINDEX_UTF_32:
        if (RSTRING_LEN(str) < 4) break;
        q = (const unsigned char *)RSTRING_PTR(str);
        if (q[0] == 0 && q[1] == 0 && q[2] == 0xFE && q[3] == 0xFF) {
            return rb_enc_get_from_index(ENCINDEX_UTF_32BE);
        }
        if (q[3] == 0 && q[2] == 0 && q[1] == 0xFE && q[0] == 0xFF) {
            return rb_enc_get_from_index(ENCINDEX_UTF_32LE);
        }
        return rb_ascii8bit_encoding();
    }
    return rb_enc_from_index(encidx);
}

static rb_encoding *
get_encoding(VALUE str)
{
    return get_actual_encoding(ENCODING_GET(str), str);
}

static int fstring_cmp(VALUE a, VALUE b);

static st_table* frozen_strings;

static const struct st_hash_type fstring_hash_type = {
    fstring_cmp,
    rb_str_hash,
};

static int
fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t arg, int existing)
{
    VALUE *fstr = (VALUE *)arg;
    VALUE str = (VALUE)*key;

    if (existing) {
        /* because of lazy sweep, str may be unmarked already and swept
         * at next time */
        rb_gc_resurrect(*fstr = *key);
        return ST_STOP;
    }

    if (STR_SHARED_P(str)) {
        /* str should not be shared */
        str = rb_enc_str_new(RSTRING_PTR(str), RSTRING_LEN(str), STR_ENC_GET(str));
        OBJ_FREEZE(str);
    }
    else {
        str = rb_str_new_frozen(str);
    }
    RBASIC(str)->flags |= RSTRING_FSTR;

    *key = *value = *fstr = str;
    return ST_CONTINUE;
}

VALUE
rb_fstring(VALUE str)
{
    VALUE fstr = Qnil;
    Check_Type(str, T_STRING);

    if (!frozen_strings)
        frozen_strings = st_init_table(&fstring_hash_type);

    if (FL_TEST(str, RSTRING_FSTR))
        return str;

    st_update(frozen_strings, (st_data_t)str, fstr_update_callback, (st_data_t)&fstr);
    return fstr;
}

static int
fstring_set_class_i(st_data_t key, st_data_t val, st_data_t arg)
{
    RBASIC_SET_CLASS((VALUE)key, (VALUE)arg);
    return ST_CONTINUE;
}

static int
fstring_cmp(VALUE a, VALUE b)
{
    int cmp = rb_str_hash_cmp(a, b);
    if (cmp != 0) {
        return cmp;
    }
    return ENCODING_GET(b) - ENCODING_GET(a);
}

static inline int
single_byte_optimizable(VALUE str)
{
    rb_encoding *enc;

    /* Conservative.  It may be ENC_CODERANGE_UNKNOWN. */
    if (ENC_CODERANGE(str) == ENC_CODERANGE_7BIT)
        return 1;

    enc = STR_ENC_GET(str);
    if (rb_enc_mbmaxlen(enc) == 1)
        return 1;

    /* Conservative.  Possibly single byte.
     * "\xa1" in Shift_JIS for example. */
    return 0;
}

VALUE rb_fs;

static inline const char *
search_nonascii(const char *p, const char *e)
{
#if SIZEOF_VALUE == 8
# define NONASCII_MASK 0x8080808080808080ULL
#elif SIZEOF_VALUE == 4
# define NONASCII_MASK 0x80808080UL
#endif
#ifdef NONASCII_MASK
    if ((int)sizeof(VALUE) * 2 < e - p) {
        const VALUE *s, *t;
        const VALUE lowbits = sizeof(VALUE) - 1;
        s = (const VALUE*)(~lowbits & ((VALUE)p + lowbits));
        while (p < (const char *)s) {
            if (!ISASCII(*p))
                return p;
            p++;
        }
        t = (const VALUE*)(~lowbits & (VALUE)e);
        while (s < t) {
            if (*s & NONASCII_MASK) {
                t = s;
                break;
            }
            s++;
        }
        p = (const char *)t;
    }
#endif
    while (p < e) {
        if (!ISASCII(*p))
            return p;
        p++;
    }
    return NULL;
}

static int
coderange_scan(const char *p, long len, rb_encoding *enc)
{
    const char *e = p + len;

    if (rb_enc_to_index(enc) == 0) {
        /* enc is ASCII-8BIT.  ASCII-8BIT string never be broken. */
        p = search_nonascii(p, e);
        return p ? ENC_CODERANGE_VALID : ENC_CODERANGE_7BIT;
    }

    if (rb_enc_asciicompat(enc)) {
        p = search_nonascii(p, e);
        if (!p) {
            return ENC_CODERANGE_7BIT;
        }
        while (p < e) {
            int ret = rb_enc_precise_mbclen(p, e, enc);
            if (!MBCLEN_CHARFOUND_P(ret)) {
                return ENC_CODERANGE_BROKEN;
            }
            p += MBCLEN_CHARFOUND_LEN(ret);
            if (p < e) {
                p = search_nonascii(p, e);
                if (!p) {
                    return ENC_CODERANGE_VALID;
                }
            }
        }
        if (e < p) {
            return ENC_CODERANGE_BROKEN;
        }
        return ENC_CODERANGE_VALID;
    }

    while (p < e) {
        int ret = rb_enc_precise_mbclen(p, e, enc);

        if (!MBCLEN_CHARFOUND_P(ret)) {
            return ENC_CODERANGE_BROKEN;
        }
        p += MBCLEN_CHARFOUND_LEN(ret);
    }
    if (e < p) {
        return ENC_CODERANGE_BROKEN;
    }
    return ENC_CODERANGE_VALID;
}

long
rb_str_coderange_scan_restartable(const char *s, const char *e, rb_encoding *enc, int *cr)
{
    const char *p = s;

    if (*cr == ENC_CODERANGE_BROKEN)
        return e - s;

    if (rb_enc_to_index(enc) == 0) {
        /* enc is ASCII-8BIT.  ASCII-8BIT string never be broken. */
        p = search_nonascii(p, e);
        *cr = (!p && *cr != ENC_CODERANGE_VALID) ? ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID;
        return e - s;
    }
    else if (rb_enc_asciicompat(enc)) {
        p = search_nonascii(p, e);
        if (!p) {
            if (*cr != ENC_CODERANGE_VALID) *cr = ENC_CODERANGE_7BIT;
            return e - s;
        }
        while (p < e) {
            int ret = rb_enc_precise_mbclen(p, e, enc);
            if (!MBCLEN_CHARFOUND_P(ret)) {
                *cr = MBCLEN_INVALID_P(ret) ? ENC_CODERANGE_BROKEN: ENC_CODERANGE_UNKNOWN;
                return p - s;
            }
            p += MBCLEN_CHARFOUND_LEN(ret);
            if (p < e) {
                p = search_nonascii(p, e);
                if (!p) {
                    *cr = ENC_CODERANGE_VALID;
                    return e - s;
                }
            }
        }
        *cr = e < p ? ENC_CODERANGE_BROKEN: ENC_CODERANGE_VALID;
        return p - s;
    }
    else {
        while (p < e) {
            int ret = rb_enc_precise_mbclen(p, e, enc);
            if (!MBCLEN_CHARFOUND_P(ret)) {
                *cr = MBCLEN_INVALID_P(ret) ? ENC_CODERANGE_BROKEN: ENC_CODERANGE_UNKNOWN;
                return p - s;
            }
            p += MBCLEN_CHARFOUND_LEN(ret);
        }
        *cr = e < p ? ENC_CODERANGE_BROKEN: ENC_CODERANGE_VALID;
        return p - s;
    }
}

static inline void
str_enc_copy(VALUE str1, VALUE str2)
{
    rb_enc_set_index(str1, ENCODING_GET(str2));
}

static void
rb_enc_cr_str_copy_for_substr(VALUE dest, VALUE src)
{
    /* this function is designed for copying encoding and coderange
     * from src to new string "dest" which is made from the part of src.
     */
    str_enc_copy(dest, src);
    if (RSTRING_LEN(dest) == 0) {
        if (!rb_enc_asciicompat(STR_ENC_GET(src)))
            ENC_CODERANGE_SET(dest, ENC_CODERANGE_VALID);
        else
            ENC_CODERANGE_SET(dest, ENC_CODERANGE_7BIT);
        return;
    }
    switch (ENC_CODERANGE(src)) {
      case ENC_CODERANGE_7BIT:
        ENC_CODERANGE_SET(dest, ENC_CODERANGE_7BIT);
        break;
      case ENC_CODERANGE_VALID:
        if (!rb_enc_asciicompat(STR_ENC_GET(src)) ||
            search_nonascii(RSTRING_PTR(dest), RSTRING_END(dest)))
            ENC_CODERANGE_SET(dest, ENC_CODERANGE_VALID);
        else
            ENC_CODERANGE_SET(dest, ENC_CODERANGE_7BIT);
        break;
      default:
        break;
    }
}

static void
rb_enc_cr_str_exact_copy(VALUE dest, VALUE src)
{
    str_enc_copy(dest, src);
    ENC_CODERANGE_SET(dest, ENC_CODERANGE(src));
}

int
rb_enc_str_coderange(VALUE str)
{
    int cr = ENC_CODERANGE(str);

    if (cr == ENC_CODERANGE_UNKNOWN) {
        rb_encoding *enc = STR_ENC_GET(str);
        cr = coderange_scan(RSTRING_PTR(str), RSTRING_LEN(str), enc);
        ENC_CODERANGE_SET(str, cr);
    }
    return cr;
}

int
rb_enc_str_asciionly_p(VALUE str)
{
    rb_encoding *enc = STR_ENC_GET(str);

    if (!rb_enc_asciicompat(enc))
        return FALSE;
    else if (rb_enc_str_coderange(str) == ENC_CODERANGE_7BIT)
        return TRUE;
    return FALSE;
}

static inline void
str_mod_check(VALUE s, const char *p, long len)
{
    if (RSTRING_PTR(s) != p || RSTRING_LEN(s) != len){
        rb_raise(rb_eRuntimeError, "string modified");
    }
}

size_t
rb_str_capacity(VALUE str)
{
    if (STR_EMBED_P(str)) {
        return RSTRING_EMBED_LEN_MAX;
    }
    else if (STR_NOCAPA_P(str)) {
        return RSTRING(str)->as.heap.len;
    }
    else {
        return RSTRING(str)->as.heap.aux.capa;
    }
}

static inline VALUE
str_alloc(VALUE klass)
{
    NEWOBJ_OF(str, struct RString, klass, T_STRING | (RGENGC_WB_PROTECTED_STRING ? FL_WB_PROTECTED : 0));
    return (VALUE)str;
}

static inline VALUE
empty_str_alloc(VALUE klass)
{
    if (RUBY_DTRACE_STRING_CREATE_ENABLED()) {
        RUBY_DTRACE_STRING_CREATE(0, rb_sourcefile(), rb_sourceline());
    }
    return str_alloc(klass);
}

static VALUE
str_new0(VALUE klass, const char *ptr, long len, int termlen)
{
    VALUE str;

    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big)");
    }

    if (RUBY_DTRACE_STRING_CREATE_ENABLED()) {
        RUBY_DTRACE_STRING_CREATE(len, rb_sourcefile(), rb_sourceline());
    }

    str = str_alloc(klass);
    if (len > RSTRING_EMBED_LEN_MAX) {
        RSTRING(str)->as.heap.aux.capa = len;
        RSTRING(str)->as.heap.ptr = ALLOC_N(char, len + termlen);
        STR_SET_NOEMBED(str);
    }
    else if (len == 0) {
        ENC_CODERANGE_SET(str, ENC_CODERANGE_7BIT);
    }
    if (ptr) {
        memcpy(RSTRING_PTR(str), ptr, len);
    }
    STR_SET_LEN(str, len);
    TERM_FILL(RSTRING_PTR(str) + len, termlen);
    return str;
}

static VALUE
str_new(VALUE klass, const char *ptr, long len)
{
    return str_new0(klass, ptr, len, 1);
}

VALUE
rb_str_new(const char *ptr, long len)
{
    return str_new(rb_cString, ptr, len);
}

VALUE
rb_usascii_str_new(const char *ptr, long len)
{
    VALUE str = rb_str_new(ptr, len);
    ENCODING_CODERANGE_SET(str, rb_usascii_encindex(), ENC_CODERANGE_7BIT);
    return str;
}

VALUE
rb_enc_str_new(const char *ptr, long len, rb_encoding *enc)
{
    VALUE str;

    if (!enc) return rb_str_new(ptr, len);

    str = str_new0(rb_cString, ptr, len, rb_enc_mbminlen(enc));
    rb_enc_associate(str, enc);
    return str;
}

VALUE
rb_str_new_cstr(const char *ptr)
{
    if (!ptr) {
        rb_raise(rb_eArgError, "NULL pointer given");
    }
    return rb_str_new(ptr, strlen(ptr));
}

VALUE
rb_usascii_str_new_cstr(const char *ptr)
{
    VALUE str = rb_str_new2(ptr);
    ENCODING_CODERANGE_SET(str, rb_usascii_encindex(), ENC_CODERANGE_7BIT);
    return str;
}

VALUE
rb_enc_str_new_cstr(const char *ptr, rb_encoding *enc)
{
    if (!ptr) {
        rb_raise(rb_eArgError, "NULL pointer given");
    }
    if (rb_enc_mbminlen(enc) != 1) {
        rb_raise(rb_eArgError, "wchar encoding given");
    }
    return rb_enc_str_new(ptr, strlen(ptr), enc);
}

VALUE
rb_tainted_str_new(const char *ptr, long len)
{
    VALUE str = rb_str_new(ptr, len);

    OBJ_TAINT(str);
    return str;
}

VALUE
rb_tainted_str_new_cstr(const char *ptr)
{
    VALUE str = rb_str_new2(ptr);

    OBJ_TAINT(str);
    return str;
}

VALUE
rb_str_conv_enc_opts(VALUE str, rb_encoding *from, rb_encoding *to, int ecflags, VALUE ecopts)
{
    extern VALUE rb_cEncodingConverter;
    rb_econv_t *ec;
    rb_econv_result_t ret;
    long len, olen;
    VALUE econv_wrapper;
    VALUE newstr;
    const unsigned char *start, *sp;
    unsigned char *dest, *dp;
    size_t converted_output = 0;

    if (!to) return str;
    if (!from) from = rb_enc_get(str);
    if (from == to) return str;
    if ((rb_enc_asciicompat(to) && is_ascii_string(str)) ||
        to == rb_ascii8bit_encoding()) {
        if (STR_ENC_GET(str) != to) {
            str = rb_str_dup(str);
            rb_enc_associate(str, to);
        }
        return str;
    }

    len = RSTRING_LEN(str);
    newstr = rb_str_new(0, len);
    OBJ_INFECT(newstr, str);
    olen = len;

    econv_wrapper = rb_obj_alloc(rb_cEncodingConverter);
    RBASIC_CLEAR_CLASS(econv_wrapper);
    ec = rb_econv_open_opts(from->name, to->name, ecflags, ecopts);
    if (!ec) return str;
    DATA_PTR(econv_wrapper) = ec;

    sp = (unsigned char*)RSTRING_PTR(str);
    start = sp;
    while ((dest = (unsigned char*)RSTRING_PTR(newstr)),
           (dp = dest + converted_output),
           (ret = rb_econv_convert(ec, &sp, start + len, &dp, dest + olen, 0)),
           ret == econv_destination_buffer_full) {
        /* destination buffer short */
        size_t converted_input = sp - start;
        size_t rest = len - converted_input;
        converted_output = dp - dest;
        rb_str_set_len(newstr, converted_output);
        if (converted_input && converted_output &&
            rest < (LONG_MAX / converted_output)) {
            rest = (rest * converted_output) / converted_input;
        }
        else {
            rest = olen;
        }
        olen += rest < 2 ? 2 : rest;
        rb_str_resize(newstr, olen);
    }
    DATA_PTR(econv_wrapper) = 0;
    rb_econv_close(ec);
    rb_gc_force_recycle(econv_wrapper);
    switch (ret) {
      case econv_finished:
        len = dp - (unsigned char*)RSTRING_PTR(newstr);
        rb_str_set_len(newstr, len);
        rb_enc_associate(newstr, to);
        return newstr;

      default:
        /* some error, return original */
        return str;
    }
}

VALUE
rb_str_conv_enc(VALUE str, rb_encoding *from, rb_encoding *to)
{
    return rb_str_conv_enc_opts(str, from, to, 0, Qnil);
}

VALUE
rb_external_str_new_with_enc(const char *ptr, long len, rb_encoding *eenc)
{
    VALUE str;

    str = rb_tainted_str_new(ptr, len);
    return rb_external_str_with_enc(str, eenc);
}

VALUE
rb_external_str_with_enc(VALUE str, rb_encoding *eenc)
{
    if (eenc == rb_usascii_encoding() &&
        rb_enc_str_coderange(str) != ENC_CODERANGE_7BIT) {
        rb_enc_associate(str, rb_ascii8bit_encoding());
        return str;
    }
    rb_enc_associate(str, eenc);
    return rb_str_conv_enc(str, eenc, rb_default_internal_encoding());
}

VALUE
rb_external_str_new(const char *ptr, long len)
{
    return rb_external_str_new_with_enc(ptr, len, rb_default_external_encoding());
}

VALUE
rb_external_str_new_cstr(const char *ptr)
{
    return rb_external_str_new_with_enc(ptr, strlen(ptr), rb_default_external_encoding());
}

VALUE
rb_locale_str_new(const char *ptr, long len)
{
    return rb_external_str_new_with_enc(ptr, len, rb_locale_encoding());
}

VALUE
rb_locale_str_new_cstr(const char *ptr)
{
    return rb_external_str_new_with_enc(ptr, strlen(ptr), rb_locale_encoding());
}

VALUE
rb_filesystem_str_new(const char *ptr, long len)
{
    return rb_external_str_new_with_enc(ptr, len, rb_filesystem_encoding());
}

VALUE
rb_filesystem_str_new_cstr(const char *ptr)
{
    return rb_external_str_new_with_enc(ptr, strlen(ptr), rb_filesystem_encoding());
}

VALUE
rb_str_export(VALUE str)
{
    return rb_str_conv_enc(str, STR_ENC_GET(str), rb_default_external_encoding());
}

VALUE
rb_str_export_locale(VALUE str)
{
    return rb_str_conv_enc(str, STR_ENC_GET(str), rb_locale_encoding());
}

VALUE
rb_str_export_to_enc(VALUE str, rb_encoding *enc)
{
    return rb_str_conv_enc(str, STR_ENC_GET(str), enc);
}

static VALUE
str_replace_shared_without_enc(VALUE str2, VALUE str)
{
    if (RSTRING_LEN(str) <= RSTRING_EMBED_LEN_MAX) {
        STR_SET_EMBED(str2);
        memcpy(RSTRING_PTR(str2), RSTRING_PTR(str), RSTRING_LEN(str)+1);
        STR_SET_EMBED_LEN(str2, RSTRING_LEN(str));
    }
    else {
        str = rb_str_new_frozen(str);
        FL_SET(str2, STR_NOEMBED);
        RSTRING(str2)->as.heap.len = RSTRING_LEN(str);
        RSTRING(str2)->as.heap.ptr = RSTRING_PTR(str);
        STR_SET_SHARED(str2, str);
    }
    return str2;
}

static VALUE
str_replace_shared(VALUE str2, VALUE str)
{
    str_replace_shared_without_enc(str2, str);
    rb_enc_cr_str_exact_copy(str2, str);
    return str2;
}

static VALUE
str_new_shared(VALUE klass, VALUE str)
{
    return str_replace_shared(str_alloc(klass), str);
}

static VALUE
str_new3(VALUE klass, VALUE str)
{
    return str_new_shared(klass, str);
}

VALUE
rb_str_new_shared(VALUE str)
{
    VALUE str2 = str_new3(rb_obj_class(str), str);

    OBJ_INFECT(str2, str);
    return str2;
}

static VALUE
str_new4(VALUE klass, VALUE str)
{
    VALUE str2;

    str2 = str_alloc(klass);
    STR_SET_NOEMBED(str2);
    RSTRING(str2)->as.heap.len = RSTRING_LEN(str);
    RSTRING(str2)->as.heap.ptr = RSTRING_PTR(str);
    if (STR_SHARED_P(str)) {
        VALUE shared = RSTRING(str)->as.heap.aux.shared;
        assert(OBJ_FROZEN(shared));
        STR_SET_SHARED(str2, shared); /* TODO: WB is not needed because str2 is *new* object */
    }
    else {
        if (!STR_ASSOC_P(str)) {
            RSTRING(str2)->as.heap.aux.capa = RSTRING(str)->as.heap.aux.capa;
        }
        STR_SET_SHARED(str, str2);
    }
    rb_enc_cr_str_exact_copy(str2, str);
    OBJ_INFECT(str2, str);
    return str2;
}

VALUE
rb_str_new_frozen(VALUE orig)
{
    VALUE klass, str;

    if (OBJ_FROZEN(orig)) return orig;
    klass = rb_obj_class(orig);
    if (STR_SHARED_P(orig) && (str = RSTRING(orig)->as.heap.aux.shared)) {
        long ofs;
        assert(OBJ_FROZEN(str));
        ofs = RSTRING_LEN(str) - RSTRING_LEN(orig);
        if ((ofs > 0) || (klass != RBASIC(str)->klass) ||
            ((RBASIC(str)->flags ^ RBASIC(orig)->flags) & FL_TAINT) ||
            ENCODING_GET(str) != ENCODING_GET(orig)) {
            str = str_new3(klass, str);
            RSTRING(str)->as.heap.ptr += ofs;
            RSTRING(str)->as.heap.len -= ofs;
            rb_enc_cr_str_exact_copy(str, orig);
            OBJ_INFECT(str, orig);
        }
    }
    else if (STR_EMBED_P(orig)) {
        str = str_new(klass, RSTRING_PTR(orig), RSTRING_LEN(orig));
        rb_enc_cr_str_exact_copy(str, orig);
        OBJ_INFECT(str, orig);
    }
    else if (STR_ASSOC_P(orig)) {
        VALUE assoc = RSTRING(orig)->as.heap.aux.shared;
        FL_UNSET(orig, STR_ASSOC);
        str = str_new4(klass, orig);
        FL_SET(str, STR_ASSOC);
        RB_OBJ_WRITE(str, &RSTRING(str)->as.heap.aux.shared, assoc);
        /* TODO: WB is not needed because str is new object */
    }
    else {
        str = str_new4(klass, orig);
    }
    OBJ_FREEZE(str);
    return str;
}

VALUE
rb_str_new_with_class(VALUE obj, const char *ptr, long len)
{
    return str_new(rb_obj_class(obj), ptr, len);
}

static VALUE
str_new_empty(VALUE str)
{
    VALUE v = rb_str_new5(str, 0, 0);
    rb_enc_copy(v, str);
    OBJ_INFECT(v, str);
    return v;
}

#define STR_BUF_MIN_SIZE 128

VALUE
rb_str_buf_new(long capa)
{
    VALUE str = str_alloc(rb_cString);

    if (capa < STR_BUF_MIN_SIZE) {
        capa = STR_BUF_MIN_SIZE;
    }
    FL_SET(str, STR_NOEMBED);
    RSTRING(str)->as.heap.aux.capa = capa;
    RSTRING(str)->as.heap.ptr = ALLOC_N(char, capa+1);
    RSTRING(str)->as.heap.ptr[0] = '\0';

    return str;
}

VALUE
rb_str_buf_new_cstr(const char *ptr)
{
    VALUE str;
    long len = strlen(ptr);

    str = rb_str_buf_new(len);
    rb_str_buf_cat(str, ptr, len);

    return str;
}

VALUE
rb_str_tmp_new(long len)
{
    return str_new(0, 0, len);
}

void *
rb_alloc_tmp_buffer(volatile VALUE *store, long len)
{
    VALUE s = rb_str_tmp_new(len);
    *store = s;
    return RSTRING_PTR(s);
}

void
rb_free_tmp_buffer(volatile VALUE *store)
{
    VALUE s = *store;
    *store = 0;
    if (s) rb_str_clear(s);
}

void
rb_str_free(VALUE str)
{
    if (FL_TEST(str, RSTRING_FSTR)) {
        st_data_t fstr = (st_data_t)str;
        st_delete(frozen_strings, &fstr, NULL);
    }
    if (!STR_EMBED_P(str) && !STR_SHARED_P(str)) {
        ruby_sized_xfree(STR_HEAP_PTR(str), STR_HEAP_SIZE(str));
    }
}

RUBY_FUNC_EXPORTED size_t
rb_str_memsize(VALUE str)
{
    if (FL_TEST(str, STR_NOEMBED|ELTS_SHARED) == STR_NOEMBED) {
        return STR_HEAP_SIZE(str);
    }
    else {
        return 0;
    }
}

VALUE
rb_str_to_str(VALUE str)
{
    return rb_convert_type(str, T_STRING, "String", "to_str");
}

static inline void str_discard(VALUE str);

void
rb_str_shared_replace(VALUE str, VALUE str2)
{
    rb_encoding *enc;
    int cr;
    if (str == str2) return;
    enc = STR_ENC_GET(str2);
    cr = ENC_CODERANGE(str2);
    str_discard(str);
    OBJ_INFECT(str, str2);
    if (RSTRING_LEN(str2) <= RSTRING_EMBED_LEN_MAX) {
        STR_SET_EMBED(str);
        memcpy(RSTRING_PTR(str), RSTRING_PTR(str2), RSTRING_LEN(str2)+1);
        STR_SET_EMBED_LEN(str, RSTRING_LEN(str2));
        rb_enc_associate(str, enc);
        ENC_CODERANGE_SET(str, cr);
        return;
    }
    STR_SET_NOEMBED(str);
    STR_UNSET_NOCAPA(str);
    RSTRING(str)->as.heap.ptr = RSTRING_PTR(str2);
    RSTRING(str)->as.heap.len = RSTRING_LEN(str2);
    if (STR_NOCAPA_P(str2)) {
        VALUE shared = RSTRING(str2)->as.heap.aux.shared;
        FL_SET(str, RBASIC(str2)->flags & STR_NOCAPA);
        RB_OBJ_WRITE(str, &RSTRING(str)->as.heap.aux.shared, shared);
    }
    else {
        RSTRING(str)->as.heap.aux.capa = RSTRING(str2)->as.heap.aux.capa;
    }
    STR_SET_EMBED(str2);        /* abandon str2 */
    RSTRING_PTR(str2)[0] = 0;
    STR_SET_EMBED_LEN(str2, 0);
    rb_enc_associate(str, enc);
    ENC_CODERANGE_SET(str, cr);
}

static ID id_to_s;

VALUE
rb_obj_as_string(VALUE obj)
{
    VALUE str;

    if (RB_TYPE_P(obj, T_STRING)) {
        return obj;
    }
    str = rb_funcall(obj, id_to_s, 0);
    if (!RB_TYPE_P(str, T_STRING))
        return rb_any_to_s(obj);
    OBJ_INFECT(str, obj);
    return str;
}

static VALUE
str_replace(VALUE str, VALUE str2)
{
    long len;

    len = RSTRING_LEN(str2);
    if (STR_ASSOC_P(str2)) {
        str2 = rb_str_new4(str2);
    }
    if (STR_SHARED_P(str2)) {
        VALUE shared = RSTRING(str2)->as.heap.aux.shared;
        assert(OBJ_FROZEN(shared));
        STR_SET_NOEMBED(str);
        RSTRING(str)->as.heap.len = len;
        RSTRING(str)->as.heap.ptr = RSTRING_PTR(str2);
        FL_SET(str, ELTS_SHARED);
        FL_UNSET(str, STR_ASSOC);
        STR_SET_SHARED(str, shared);
    }
    else {
        str_replace_shared(str, str2);
    }

    OBJ_INFECT(str, str2);
    rb_enc_cr_str_exact_copy(str, str2);
    return str;
}

static VALUE
str_duplicate(VALUE klass, VALUE str)
{
    VALUE dup = str_alloc(klass);
    str_replace(dup, str);
    return dup;
}

VALUE
rb_str_dup(VALUE str)
{
    return str_duplicate(rb_obj_class(str), str);
}

VALUE
rb_str_resurrect(VALUE str)
{
    if (RUBY_DTRACE_STRING_CREATE_ENABLED()) {
        RUBY_DTRACE_STRING_CREATE(RSTRING_LEN(str),
                                  rb_sourcefile(), rb_sourceline());
    }
    return str_duplicate(rb_cString, str);
}

/*
 *  call-seq:
 *     String.new(str="")   -> new_str
 *
 *  Returns a new string object containing a copy of <i>str</i>.
 */

static VALUE
rb_str_init(int argc, VALUE *argv, VALUE str)
{
    VALUE orig;

    if (argc > 0 && rb_scan_args(argc, argv, "01", &orig) == 1)
        rb_str_replace(str, orig);
    return str;
}

static inline long
enc_strlen(const char *p, const char *e, rb_encoding *enc, int cr)
{
    long c;
    const char *q;

    if (rb_enc_mbmaxlen(enc) == rb_enc_mbminlen(enc)) {
        return (e - p + rb_enc_mbminlen(enc) - 1) / rb_enc_mbminlen(enc);
    }
    else if (rb_enc_asciicompat(enc)) {
        c = 0;
        if (cr == ENC_CODERANGE_7BIT || cr == ENC_CODERANGE_VALID) {
            while (p < e) {
                if (ISASCII(*p)) {
                    q = search_nonascii(p, e);
                    if (!q)
                        return c + (e - p);
                    c += q - p;
                    p = q;
                }
                p += rb_enc_fast_mbclen(p, e, enc);
                c++;
            }
        }
        else {
            while (p < e) {
                if (ISASCII(*p)) {
                    q = search_nonascii(p, e);
                    if (!q)
                        return c + (e - p);
                    c += q - p;
                    p = q;
                }
                p += rb_enc_mbclen(p, e, enc);
                c++;
            }
        }
        return c;
    }

    for (c=0; p<e; c++) {
        p += rb_enc_mbclen(p, e, enc);
    }
    return c;
}

long
rb_enc_strlen(const char *p, const char *e, rb_encoding *enc)
{
    return enc_strlen(p, e, enc, ENC_CODERANGE_UNKNOWN);
}

long
rb_enc_strlen_cr(const char *p, const char *e, rb_encoding *enc, int *cr)
{
    long c;
    const char *q;
    int ret;

    *cr = 0;
    if (rb_enc_mbmaxlen(enc) == rb_enc_mbminlen(enc)) {
        return (e - p + rb_enc_mbminlen(enc) - 1) / rb_enc_mbminlen(enc);
    }
    else if (rb_enc_asciicompat(enc)) {
        c = 0;
        while (p < e) {
            if (ISASCII(*p)) {
                q = search_nonascii(p, e);
                if (!q) {
                    if (!*cr) *cr = ENC_CODERANGE_7BIT;
                    return c + (e - p);
                }
                c += q - p;
                p = q;
            }
            ret = rb_enc_precise_mbclen(p, e, enc);
            if (MBCLEN_CHARFOUND_P(ret)) {
                *cr |= ENC_CODERANGE_VALID;
                p += MBCLEN_CHARFOUND_LEN(ret);
            }
            else {
                *cr = ENC_CODERANGE_BROKEN;
                p++;
            }
            c++;
        }
        if (!*cr) *cr = ENC_CODERANGE_7BIT;
        return c;
    }

    for (c=0; p<e; c++) {
        ret = rb_enc_precise_mbclen(p, e, enc);
        if (MBCLEN_CHARFOUND_P(ret)) {
            *cr |= ENC_CODERANGE_VALID;
            p += MBCLEN_CHARFOUND_LEN(ret);
        }
        else {
            *cr = ENC_CODERANGE_BROKEN;
            if (p + rb_enc_mbminlen(enc) <= e)
                p += rb_enc_mbminlen(enc);
            else
                p = e;
        }
    }
    if (!*cr) *cr = ENC_CODERANGE_7BIT;
    return c;
}

#ifdef NONASCII_MASK
#define is_utf8_lead_byte(c) (((c)&0xC0) != 0x80)

/*
 * UTF-8 leading bytes have either 0xxxxxxx or 11xxxxxx
 * bit representation. (see http://en.wikipedia.org/wiki/UTF-8)
 * Therefore, following pseudo code can detect UTF-8 leading byte.
 *
 * if (!(byte & 0x80))
 *   byte |= 0x40;          // turn on bit6
 * return ((byte>>6) & 1);  // bit6 represent it's leading byte or not.
 *
 * This function calculate every bytes in the argument word `s'
 * using the above logic concurrently. and gather every bytes result.
 */
static inline VALUE
count_utf8_lead_bytes_with_word(const VALUE *s)
{
    VALUE d = *s;

    /* Transform into bit0 represent UTF-8 leading or not. */
    d |= ~(d>>1);
    d >>= 6;
    d &= NONASCII_MASK >> 7;

    /* Gather every bytes. */
    d += (d>>8);
    d += (d>>16);
#if SIZEOF_VALUE == 8
    d += (d>>32);
#endif
    return (d&0xF);
}
#endif

static long
str_strlen(VALUE str, rb_encoding *enc)
{
    const char *p, *e;
    long n;
    int cr;

    if (single_byte_optimizable(str)) return RSTRING_LEN(str);
    if (!enc) enc = STR_ENC_GET(str);
    p = RSTRING_PTR(str);
    e = RSTRING_END(str);
    cr = ENC_CODERANGE(str);
#ifdef NONASCII_MASK
    if (ENC_CODERANGE(str) == ENC_CODERANGE_VALID &&
        enc == rb_utf8_encoding()) {

        VALUE len = 0;
        if ((int)sizeof(VALUE) * 2 < e - p) {
            const VALUE *s, *t;
            const VALUE lowbits = sizeof(VALUE) - 1;
            s = (const VALUE*)(~lowbits & ((VALUE)p + lowbits));
            t = (const VALUE*)(~lowbits & (VALUE)e);
            while (p < (const char *)s) {
                if (is_utf8_lead_byte(*p)) len++;
                p++;
            }
            while (s < t) {
                len += count_utf8_lead_bytes_with_word(s);
                s++;
            }
            p = (const char *)s;
        }
        while (p < e) {
            if (is_utf8_lead_byte(*p)) len++;
            p++;
        }
        return (long)len;
    }
#endif
    n = rb_enc_strlen_cr(p, e, enc, &cr);
    if (cr) {
        ENC_CODERANGE_SET(str, cr);
    }
    return n;
}

long
rb_str_strlen(VALUE str)
{
    return str_strlen(str, STR_ENC_GET(str));
}

/*
 *  call-seq:
 *     str.length   -> integer
 *     str.size     -> integer
 *
 *  Returns the character length of <i>str</i>.
 */

VALUE
rb_str_length(VALUE str)
{
    long len;

    len = str_strlen(str, STR_ENC_GET(str));
    return LONG2NUM(len);
}

/*
 *  call-seq:
 *     str.bytesize  -> integer
 *
 *  Returns the length of +str+ in bytes.
 *
 *    "\x80\u3042".bytesize  #=> 4
 *    "hello".bytesize       #=> 5
 */

static VALUE
rb_str_bytesize(VALUE str)
{
    return LONG2NUM(RSTRING_LEN(str));
}

/*
 *  call-seq:
 *     str.empty?   -> true or false
 *
 *  Returns <code>true</code> if <i>str</i> has a length of zero.
 *
 *     "hello".empty?   #=> false
 *     " ".empty?       #=> false
 *     "".empty?        #=> true
 */

static VALUE
rb_str_empty(VALUE str)
{
    if (RSTRING_LEN(str) == 0)
        return Qtrue;
    return Qfalse;
}

/*
 *  call-seq:
 *     str + other_str   -> new_str
 *
 *  Concatenation---Returns a new <code>String</code> containing
 *  <i>other_str</i> concatenated to <i>str</i>.
 *
 *     "Hello from " + self.to_s   #=> "Hello from main"
 */

VALUE
rb_str_plus(VALUE str1, VALUE str2)
{
    VALUE str3;
    rb_encoding *enc;

    StringValue(str2);
    enc = rb_enc_check(str1, str2);
    str3 = rb_str_new(0, RSTRING_LEN(str1)+RSTRING_LEN(str2));
    memcpy(RSTRING_PTR(str3), RSTRING_PTR(str1), RSTRING_LEN(str1));
    memcpy(RSTRING_PTR(str3) + RSTRING_LEN(str1),
           RSTRING_PTR(str2), RSTRING_LEN(str2));
    RSTRING_PTR(str3)[RSTRING_LEN(str3)] = '\0';

    FL_SET_RAW(str3, OBJ_TAINTED_RAW(str1) | OBJ_TAINTED_RAW(str2));
    ENCODING_CODERANGE_SET(str3, rb_enc_to_index(enc),
                           ENC_CODERANGE_AND(ENC_CODERANGE(str1), ENC_CODERANGE(str2)));
    return str3;
}

/*
 *  call-seq:
 *     str * integer   -> new_str
 *
 *  Copy --- Returns a new String containing +integer+ copies of the receiver.
 *  +integer+ must be greater than or equal to 0.
 *
 *     "Ho! " * 3   #=> "Ho! Ho! Ho! "
 *     "Ho! " * 0   #=> ""
 */

VALUE
rb_str_times(VALUE str, VALUE times)
{
    VALUE str2;
    long n, len;
    char *ptr2;

    len = NUM2LONG(times);
    if (len < 0) {
        rb_raise(rb_eArgError, "negative argument");
    }
    if (len && LONG_MAX/len <  RSTRING_LEN(str)) {
        rb_raise(rb_eArgError, "argument too big");
    }

    str2 = rb_str_new5(str, 0, len *= RSTRING_LEN(str));
    ptr2 = RSTRING_PTR(str2);
    if (len) {
        n = RSTRING_LEN(str);
        memcpy(ptr2, RSTRING_PTR(str), n);
        while (n <= len/2) {
            memcpy(ptr2 + n, ptr2, n);
            n *= 2;
        }
        memcpy(ptr2 + n, ptr2, len-n);
    }
    ptr2[RSTRING_LEN(str2)] = '\0';
    OBJ_INFECT(str2, str);
    rb_enc_cr_str_copy_for_substr(str2, str);

    return str2;
}

/*
 *  call-seq:
 *     str % arg   -> new_str
 *
 *  Format---Uses <i>str</i> as a format specification, and returns the result
 *  of applying it to <i>arg</i>. If the format specification contains more than
 *  one substitution, then <i>arg</i> must be an <code>Array</code> or <code>Hash</code>
 *  containing the values to be substituted. See <code>Kernel::sprintf</code> for
 *  details of the format string.
 *
 *     "%05d" % 123                              #=> "00123"
 *     "%-5s: %08x" % [ "ID", self.object_id ]   #=> "ID   : 200e14d6"
 *     "foo = %{foo}" % { :foo => 'bar' }        #=> "foo = bar"
 */

static VALUE
rb_str_format_m(VALUE str, VALUE arg)
{
    volatile VALUE tmp = rb_check_array_type(arg);

    if (!NIL_P(tmp)) {
        return rb_str_format(RARRAY_LENINT(tmp), RARRAY_CONST_PTR(tmp), str);
    }
    return rb_str_format(1, &arg, str);
}

static inline void
str_modifiable(VALUE str)
{
    if (FL_TEST(str, STR_TMPLOCK)) {
        rb_raise(rb_eRuntimeError, "can't modify string; temporarily locked");
    }
    rb_check_frozen(str);
}

static inline int
str_independent(VALUE str)
{
    str_modifiable(str);
    if (!STR_SHARED_P(str)) return 1;
    if (STR_EMBED_P(str)) return 1;
    return 0;
}

static void
str_make_independent_expand(VALUE str, long expand)
{
    char *ptr;
    long len = RSTRING_LEN(str);
    const int termlen = TERM_LEN(str);
    long capa = len + expand;

    if (len > capa) len = capa;
    ptr = ALLOC_N(char, capa + termlen);
    if (RSTRING_PTR(str)) {
        memcpy(ptr, RSTRING_PTR(str), len);
    }
    STR_SET_NOEMBED(str);
    STR_UNSET_NOCAPA(str);
    TERM_FILL(ptr + len, termlen);
    RSTRING(str)->as.heap.ptr = ptr;
    RSTRING(str)->as.heap.len = len;
    RSTRING(str)->as.heap.aux.capa = capa;
}

#define str_make_independent(str) str_make_independent_expand((str), 0L)

void
rb_str_modify(VALUE str)
{
    if (!str_independent(str))
        str_make_independent(str);
    ENC_CODERANGE_CLEAR(str);
}

void
rb_str_modify_expand(VALUE str, long expand)
{
    if (expand < 0) {
        rb_raise(rb_eArgError, "negative expanding string size");
    }
    if (!str_independent(str)) {
        str_make_independent_expand(str, expand);
    }
    else if (expand > 0) {
        long len = RSTRING_LEN(str);
        long capa = len + expand;
        int termlen = TERM_LEN(str);
        if (!STR_EMBED_P(str)) {
            REALLOC_N(RSTRING(str)->as.heap.ptr, char, capa + termlen);
            STR_UNSET_NOCAPA(str);
            RSTRING(str)->as.heap.aux.capa = capa;
        }
        else if (capa + termlen > RSTRING_EMBED_LEN_MAX + 1) {
            str_make_independent_expand(str, expand);
        }
    }
    ENC_CODERANGE_CLEAR(str);
}

/* As rb_str_modify(), but don't clear coderange */
static void
str_modify_keep_cr(VALUE str)
{
    if (!str_independent(str))
        str_make_independent(str);
    if (ENC_CODERANGE(str) == ENC_CODERANGE_BROKEN)
        /* Force re-scan later */
        ENC_CODERANGE_CLEAR(str);
}

static inline void
str_discard(VALUE str)
{
    str_modifiable(str);
    if (!STR_SHARED_P(str) && !STR_EMBED_P(str)) {
        ruby_sized_xfree(STR_HEAP_PTR(str), STR_HEAP_SIZE(str));
        RSTRING(str)->as.heap.ptr = 0;
        RSTRING(str)->as.heap.len = 0;
    }
}

void
rb_str_associate(VALUE str, VALUE add)
{
    /* sanity check */
    rb_check_frozen(str);
    if (STR_ASSOC_P(str)) {
        /* already associated */
        rb_ary_concat(RSTRING(str)->as.heap.aux.shared, add);
    }
    else {
        if (STR_SHARED_P(str)) {
            VALUE assoc = RSTRING(str)->as.heap.aux.shared;
            str_make_independent(str);
            if (STR_ASSOC_P(assoc)) {
                assoc = RSTRING(assoc)->as.heap.aux.shared;
                rb_ary_concat(assoc, add);
                add = assoc;
            }
        }
        else if (STR_EMBED_P(str)) {
            str_make_independent(str);
        }
        else if (RSTRING(str)->as.heap.aux.capa != RSTRING_LEN(str)) {
            RESIZE_CAPA(str, RSTRING_LEN(str));
        }
        FL_SET(str, STR_ASSOC);
        RBASIC_CLEAR_CLASS(add);
        RB_OBJ_WRITE(str, &RSTRING(str)->as.heap.aux.shared, add);
    }
}

VALUE
rb_str_associated(VALUE str)
{
    if (STR_SHARED_P(str)) str = RSTRING(str)->as.heap.aux.shared;
    if (STR_ASSOC_P(str)) {
        return RSTRING(str)->as.heap.aux.shared;
    }
    return Qfalse;
}

void
rb_must_asciicompat(VALUE str)
{
    rb_encoding *enc = rb_enc_get(str);
    if (!rb_enc_asciicompat(enc)) {
        rb_raise(rb_eEncCompatError, "ASCII incompatible encoding: %s", rb_enc_name(enc));
    }
}

VALUE
rb_string_value(volatile VALUE *ptr)
{
    VALUE s = *ptr;
    if (!RB_TYPE_P(s, T_STRING)) {
        s = rb_str_to_str(s);
        *ptr = s;
    }
    return s;
}

char *
rb_string_value_ptr(volatile VALUE *ptr)
{
    VALUE str = rb_string_value(ptr);
    return RSTRING_PTR(str);
}

static int
zero_filled(const char *s, int n)
{
    for (; n > 0; --n) {
        if (*s++) return 0;
    }
    return 1;
}

static const char *
str_null_char(const char *s, long len, const int minlen, rb_encoding *enc)
{
    const char *e = s + len;

    for (; s + minlen <= e; s += rb_enc_mbclen(s, e, enc)) {
        if (zero_filled(s, minlen)) return s;
    }
    return 0;
}

static char *
str_fill_term(VALUE str, char *s, long len, int oldtermlen, int termlen)
{
    long capa = rb_str_capacity(str) + 1;

    if (capa < len + termlen) {
        rb_str_modify_expand(str, termlen);
    }
    else if (!str_independent(str)) {
        if (zero_filled(s + len, termlen)) return s;
        str_make_independent(str);
    }
    s = RSTRING_PTR(str);
    TERM_FILL(s + len, termlen);
    return s;
}

char *
rb_string_value_cstr(volatile VALUE *ptr)
{
    VALUE str = rb_string_value(ptr);
    char *s = RSTRING_PTR(str);
    long len = RSTRING_LEN(str);
    rb_encoding *enc = rb_enc_get(str);
    const int minlen = rb_enc_mbminlen(enc);

    if (minlen > 1) {
        if (str_null_char(s, len, minlen, enc)) {
            rb_raise(rb_eArgError, "string contains null char");
        }
        return str_fill_term(str, s, len, minlen, minlen);
    }
    if (!s || memchr(s, 0, len)) {
        rb_raise(rb_eArgError, "string contains null byte");
    }
    if (s[len]) {
        rb_str_modify(str);
        s = RSTRING_PTR(str);
        s[RSTRING_LEN(str)] = 0;
    }
    return s;
}

void
rb_str_fill_terminator(VALUE str, const int newminlen)
{
    char *s = RSTRING_PTR(str);
    long len = RSTRING_LEN(str);
    rb_encoding *enc = rb_enc_get(str);
    str_fill_term(str, s, len, rb_enc_mbminlen(enc), newminlen);
}

VALUE
rb_check_string_type(VALUE str)
{
    str = rb_check_convert_type(str, T_STRING, "String", "to_str");
    return str;
}

/*
 *  call-seq:
 *     String.try_convert(obj) -> string or nil
 *
 *  Try to convert <i>obj</i> into a String, using to_str method.
 *  Returns converted string or nil if <i>obj</i> cannot be converted
 *  for any reason.
 *
 *     String.try_convert("str")     #=> "str"
 *     String.try_convert(/re/)      #=> nil
 */
static VALUE
rb_str_s_try_convert(VALUE dummy, VALUE str)
{
    return rb_check_string_type(str);
}

static char*
str_nth_len(const char *p, const char *e, long *nthp, rb_encoding *enc)
{
    long nth = *nthp;
    if (rb_enc_mbmaxlen(enc) == 1) {
        p += nth;
    }
    else if (rb_enc_mbmaxlen(enc) == rb_enc_mbminlen(enc)) {
        p += nth * rb_enc_mbmaxlen(enc);
    }
    else if (rb_enc_asciicompat(enc)) {
        const char *p2, *e2;
        int n;

        while (p < e && 0 < nth) {
            e2 = p + nth;
            if (e < e2) {
                *nthp = nth;
                return (char *)e;
            }
            if (ISASCII(*p)) {
                p2 = search_nonascii(p, e2);
                if (!p2) {
                    nth -= e2 - p;
                    *nthp = nth;
                    return (char *)e2;
                }
                nth -= p2 - p;
                p = p2;
            }
            n = rb_enc_mbclen(p, e, enc);
            p += n;
            nth--;
        }
        *nthp = nth;
        if (nth != 0) {
            return (char *)e;
        }
        return (char *)p;
    }
    else {
        while (p < e && nth--) {
            p += rb_enc_mbclen(p, e, enc);
        }
    }
    if (p > e) p = e;
    *nthp = nth;
    return (char*)p;
}

char*
rb_enc_nth(const char *p, const char *e, long nth, rb_encoding *enc)
{
    return str_nth_len(p, e, &nth, enc);
}

static char*
str_nth(const char *p, const char *e, long nth, rb_encoding *enc, int singlebyte)
{
    if (singlebyte)
        p += nth;
    else {
        p = str_nth_len(p, e, &nth, enc);
    }
    if (!p) return 0;
    if (p > e) p = e;
    return (char *)p;
}

/* char offset to byte offset */
static long
str_offset(const char *p, const char *e, long nth, rb_encoding *enc, int singlebyte)
{
    const char *pp = str_nth(p, e, nth, enc, singlebyte);
    if (!pp) return e - p;
    return pp - p;
}

long
rb_str_offset(VALUE str, long pos)
{
    return str_offset(RSTRING_PTR(str), RSTRING_END(str), pos,
                      STR_ENC_GET(str), single_byte_optimizable(str));
}

#ifdef NONASCII_MASK
static char *
str_utf8_nth(const char *p, const char *e, long *nthp)
{
    long nth = *nthp;
    if ((int)SIZEOF_VALUE * 2 < e - p && (int)SIZEOF_VALUE * 2 < nth) {
        const VALUE *s, *t;
        const VALUE lowbits = sizeof(VALUE) - 1;
        s = (const VALUE*)(~lowbits & ((VALUE)p + lowbits));
        t = (const VALUE*)(~lowbits & (VALUE)e);
        while (p < (const char *)s) {
            if (is_utf8_lead_byte(*p)) nth--;
            p++;
        }
        do {
            nth -= count_utf8_lead_bytes_with_word(s);
            s++;
        } while (s < t && (int)sizeof(VALUE) <= nth);
        p = (char *)s;
    }
    while (p < e) {
        if (is_utf8_lead_byte(*p)) {
            if (nth == 0) break;
            nth--;
        }
        p++;
    }
    *nthp = nth;
    return (char *)p;
}

static long
str_utf8_offset(const char *p, const char *e, long nth)
{
    const char *pp = str_utf8_nth(p, e, &nth);
    return pp - p;
}
#endif

/* byte offset to char offset */
long
rb_str_sublen(VALUE str, long pos)
{
    if (single_byte_optimizable(str) || pos < 0)
        return pos;
    else {
        char *p = RSTRING_PTR(str);
        return enc_strlen(p, p + pos, STR_ENC_GET(str), ENC_CODERANGE(str));
    }
}

VALUE
rb_str_subseq(VALUE str, long beg, long len)
{
    VALUE str2;

    if (RSTRING_LEN(str) == beg + len &&
        RSTRING_EMBED_LEN_MAX < len) {
        str2 = rb_str_new_shared(rb_str_new_frozen(str));
        rb_str_drop_bytes(str2, beg);
    }
    else {
        str2 = rb_str_new5(str, RSTRING_PTR(str)+beg, len);
        RB_GC_GUARD(str);
    }

    rb_enc_cr_str_copy_for_substr(str2, str);
    OBJ_INFECT(str2, str);

    return str2;
}

char *
rb_str_subpos(VALUE str, long beg, long *lenp)
{
    long len = *lenp;
    long slen = -1L;
    long blen = RSTRING_LEN(str);
    rb_encoding *enc = STR_ENC_GET(str);
    char *p, *s = RSTRING_PTR(str), *e = s + blen;

    if (len < 0) return 0;
    if (!blen) {
        len = 0;
    }
    if (single_byte_optimizable(str)) {
        if (beg > blen) return 0;
        if (beg < 0) {
            beg += blen;
            if (beg < 0) return 0;
        }
        if (beg + len > blen)
            len = blen - beg;
        if (len < 0) return 0;
        p = s + beg;
        goto end;
    }
    if (beg < 0) {
        if (len > -beg) len = -beg;
        if (-beg * rb_enc_mbmaxlen(enc) < RSTRING_LEN(str) / 8) {
            beg = -beg;
            while (beg-- > len && (e = rb_enc_prev_char(s, e, e, enc)) != 0);
            p = e;
            if (!p) return 0;
            while (len-- > 0 && (p = rb_enc_prev_char(s, p, e, enc)) != 0);
            if (!p) return 0;
            len = e - p;
            goto end;
        }
        else {
            slen = str_strlen(str, enc);
            beg += slen;
            if (beg < 0) return 0;
            p = s + beg;
            if (len == 0) goto end;
        }
    }
    else if (beg > 0 && beg > RSTRING_LEN(str)) {
        return 0;
    }
    if (len == 0) {
        if (beg > str_strlen(str, enc)) return 0;
        p = s + beg;
    }
#ifdef NONASCII_MASK
    else if (ENC_CODERANGE(str) == ENC_CODERANGE_VALID &&
        enc == rb_utf8_encoding()) {
        p = str_utf8_nth(s, e, &beg);
        if (beg > 0) return 0;
        len = str_utf8_offset(p, e, len);
    }
#endif
    else if (rb_enc_mbmaxlen(enc) == rb_enc_mbminlen(enc)) {
        int char_sz = rb_enc_mbmaxlen(enc);

        p = s + beg * char_sz;
        if (p > e) {
            return 0;
        }
        else if (len * char_sz > e - p)
            len = e - p;
        else
            len *= char_sz;
    }
    else if ((p = str_nth_len(s, e, &beg, enc)) == e) {
        if (beg > 0) return 0;
        len = 0;
    }
    else {
        len = str_offset(p, e, len, enc, 0);
    }
  end:
    *lenp = len;
    RB_GC_GUARD(str);
    return p;
}

VALUE
rb_str_substr(VALUE str, long beg, long len)
{
    VALUE str2;
    char *p = rb_str_subpos(str, beg, &len);

    if (!p) return Qnil;
    if (len > RSTRING_EMBED_LEN_MAX && p + len == RSTRING_END(str)) {
        str2 = rb_str_new4(str);
        str2 = str_new3(rb_obj_class(str2), str2);
        RSTRING(str2)->as.heap.ptr += RSTRING(str2)->as.heap.len - len;
        RSTRING(str2)->as.heap.len = len;
    }
    else {
        str2 = rb_str_new5(str, p, len);
        OBJ_INFECT(str2, str);
        RB_GC_GUARD(str);
    }
    rb_enc_cr_str_copy_for_substr(str2, str);

    return str2;
}

VALUE
rb_str_freeze(VALUE str)
{
    if (STR_ASSOC_P(str)) {
        VALUE ary = RSTRING(str)->as.heap.aux.shared;
        OBJ_FREEZE(ary);
    }
    return rb_obj_freeze(str);
}

RUBY_ALIAS_FUNCTION(rb_str_dup_frozen(VALUE str), rb_str_new_frozen, (str))
#define rb_str_dup_frozen rb_str_new_frozen

VALUE
rb_str_locktmp(VALUE str)
{
    if (FL_TEST(str, STR_TMPLOCK)) {
        rb_raise(rb_eRuntimeError, "temporal locking already locked string");
    }
    FL_SET(str, STR_TMPLOCK);
    return str;
}

VALUE
rb_str_unlocktmp(VALUE str)
{
    if (!FL_TEST(str, STR_TMPLOCK)) {
        rb_raise(rb_eRuntimeError, "temporal unlocking already unlocked string");
    }
    FL_UNSET(str, STR_TMPLOCK);
    return str;
}

VALUE
rb_str_locktmp_ensure(VALUE str, VALUE (*func)(VALUE), VALUE arg)
{
    rb_str_locktmp(str);
    return rb_ensure(func, arg, rb_str_unlocktmp, str);
}

void
rb_str_set_len(VALUE str, long len)
{
    long capa;
    const int termlen = TERM_LEN(str);

    str_modifiable(str);
    if (STR_SHARED_P(str)) {
        rb_raise(rb_eRuntimeError, "can't set length of shared string");
    }
    if (len + termlen - 1 > (capa = (long)rb_str_capacity(str))) {
        rb_bug("probable buffer overflow: %ld for %ld", len, capa);
    }
    STR_SET_LEN(str, len);
    TERM_FILL(&RSTRING_PTR(str)[len], termlen);
}

VALUE
rb_str_resize(VALUE str, long len)
{
    long slen;
    int independent;

    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big)");
    }

    independent = str_independent(str);
    ENC_CODERANGE_CLEAR(str);
    slen = RSTRING_LEN(str);
    {
        long capa;
        const int termlen = TERM_LEN(str);
        if (STR_EMBED_P(str)) {
            if (len == slen) return str;
            if (len + termlen <= RSTRING_EMBED_LEN_MAX + 1) {
                STR_SET_EMBED_LEN(str, len);
                TERM_FILL(RSTRING(str)->as.ary + len, termlen);
                return str;
            }
            str_make_independent_expand(str, len - slen);
            STR_SET_NOEMBED(str);
        }
        else if (len + termlen <= RSTRING_EMBED_LEN_MAX + 1) {
            char *ptr = STR_HEAP_PTR(str);
            STR_SET_EMBED(str);
            if (slen > len) slen = len;
            if (slen > 0) MEMCPY(RSTRING(str)->as.ary, ptr, char, slen);
            TERM_FILL(RSTRING(str)->as.ary + len, termlen);
            STR_SET_EMBED_LEN(str, len);
            if (independent) ruby_xfree(ptr);
            return str;
        }
        else if (!independent) {
            if (len == slen) return str;
            str_make_independent_expand(str, len - slen);
        }
        else if ((capa = RSTRING(str)->as.heap.aux.capa) < len ||
                 (capa - len) > (len < 1024 ? len : 1024)) {
            REALLOC_N(RSTRING(str)->as.heap.ptr, char, len + termlen);
            RSTRING(str)->as.heap.aux.capa = len;
        }
        else if (len == slen) return str;
        RSTRING(str)->as.heap.len = len;
        TERM_FILL(RSTRING(str)->as.heap.ptr + len, termlen); /* sentinel */
    }
    return str;
}

static VALUE
str_buf_cat(VALUE str, const char *ptr, long len)
{
    long capa, total, off = -1;
    const int termlen = TERM_LEN(str);

    if (ptr >= RSTRING_PTR(str) && ptr <= RSTRING_END(str)) {
        off = ptr - RSTRING_PTR(str);
    }
    rb_str_modify(str);
    if (len == 0) return 0;
    if (STR_ASSOC_P(str)) {
        FL_UNSET(str, STR_ASSOC);
        capa = RSTRING(str)->as.heap.aux.capa = RSTRING_LEN(str);
    }
    else if (STR_EMBED_P(str)) {
        capa = RSTRING_EMBED_LEN_MAX;
    }
    else {
        capa = RSTRING(str)->as.heap.aux.capa;
    }
    if (RSTRING_LEN(str) >= LONG_MAX - len) {
        rb_raise(rb_eArgError, "string sizes too big");
    }
    total = RSTRING_LEN(str)+len;
    if (capa <= total) {
        while (total > capa) {
            if (capa + termlen >= LONG_MAX / 2) {
                capa = (total + 4095) / 4096 * 4096;
                break;
            }
            capa = (capa + termlen) * 2;
        }
        RESIZE_CAPA(str, capa);
    }
    if (off != -1) {
        ptr = RSTRING_PTR(str) + off;
    }
    memcpy(RSTRING_PTR(str) + RSTRING_LEN(str), ptr, len);
    STR_SET_LEN(str, total);
    RSTRING_PTR(str)[total] = '\0'; /* sentinel */

    return str;
}

#define str_buf_cat2(str, ptr) str_buf_cat((str), (ptr), strlen(ptr))

VALUE
rb_str_buf_cat(VALUE str, const char *ptr, long len)
{
    if (len == 0) return str;
    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big)");
    }
    return str_buf_cat(str, ptr, len);
}

VALUE
rb_str_buf_cat2(VALUE str, const char *ptr)
{
    return rb_str_buf_cat(str, ptr, strlen(ptr));
}

VALUE
rb_str_cat(VALUE str, const char *ptr, long len)
{
    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big)");
    }
    if (STR_ASSOC_P(str)) {
        char *p;
        rb_str_modify_expand(str, len);
        p = RSTRING(str)->as.heap.ptr;
        memcpy(p + RSTRING(str)->as.heap.len, ptr, len);
        len = RSTRING(str)->as.heap.len += len;
        TERM_FILL(p, TERM_LEN(str)); /* sentinel */
        return str;
    }

    return rb_str_buf_cat(str, ptr, len);
}

VALUE
rb_str_cat2(VALUE str, const char *ptr)
{
    return rb_str_cat(str, ptr, strlen(ptr));
}

static VALUE
rb_enc_cr_str_buf_cat(VALUE str, const char *ptr, long len,
    int ptr_encindex, int ptr_cr, int *ptr_cr_ret)
{
    int str_encindex = ENCODING_GET(str);
    int res_encindex;
    int str_cr, res_cr;

    str_cr = RSTRING_LEN(str) ? ENC_CODERANGE(str) : ENC_CODERANGE_7BIT;

    if (str_encindex == ptr_encindex) {
        if (str_cr == ENC_CODERANGE_UNKNOWN)
            ptr_cr = ENC_CODERANGE_UNKNOWN;
        else if (ptr_cr == ENC_CODERANGE_UNKNOWN) {
            ptr_cr = coderange_scan(ptr, len, rb_enc_from_index(ptr_encindex));
        }
    }
    else {
        rb_encoding *str_enc = rb_enc_from_index(str_encindex);
        rb_encoding *ptr_enc = rb_enc_from_index(ptr_encindex);
        if (!rb_enc_asciicompat(str_enc) || !rb_enc_asciicompat(ptr_enc)) {
            if (len == 0)
                return str;
            if (RSTRING_LEN(str) == 0) {
                rb_str_buf_cat(str, ptr, len);
                ENCODING_CODERANGE_SET(str, ptr_encindex, ptr_cr);
                return str;
            }
            goto incompatible;
        }
        if (ptr_cr == ENC_CODERANGE_UNKNOWN) {
            ptr_cr = coderange_scan(ptr, len, ptr_enc);
        }
        if (str_cr == ENC_CODERANGE_UNKNOWN) {
            if (ENCODING_IS_ASCII8BIT(str) || ptr_cr != ENC_CODERANGE_7BIT) {
                str_cr = rb_enc_str_coderange(str);
            }
        }
    }
    if (ptr_cr_ret)
        *ptr_cr_ret = ptr_cr;

    if (str_encindex != ptr_encindex &&
        str_cr != ENC_CODERANGE_7BIT &&
        ptr_cr != ENC_CODERANGE_7BIT) {
      incompatible:
        rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
            rb_enc_name(rb_enc_from_index(str_encindex)),
            rb_enc_name(rb_enc_from_index(ptr_encindex)));
    }

    if (str_cr == ENC_CODERANGE_UNKNOWN) {
        res_encindex = str_encindex;
        res_cr = ENC_CODERANGE_UNKNOWN;
    }
    else if (str_cr == ENC_CODERANGE_7BIT) {
        if (ptr_cr == ENC_CODERANGE_7BIT) {
            res_encindex = str_encindex;
            res_cr = ENC_CODERANGE_7BIT;
        }
        else {
            res_encindex = ptr_encindex;
            res_cr = ptr_cr;
        }
    }
    else if (str_cr == ENC_CODERANGE_VALID) {
        res_encindex = str_encindex;
        if (ptr_cr == ENC_CODERANGE_7BIT || ptr_cr == ENC_CODERANGE_VALID)
            res_cr = str_cr;
        else
            res_cr = ptr_cr;
    }
    else { /* str_cr == ENC_CODERANGE_BROKEN */
        res_encindex = str_encindex;
        res_cr = str_cr;
        if (0 < len) res_cr = ENC_CODERANGE_UNKNOWN;
    }

    if (len < 0) {
        rb_raise(rb_eArgError, "negative string size (or size too big)");
    }
    str_buf_cat(str, ptr, len);
    ENCODING_CODERANGE_SET(str, res_encindex, res_cr);
    return str;
}

VALUE
rb_enc_str_buf_cat(VALUE str, const char *ptr, long len, rb_encoding *ptr_enc)
{
    return rb_enc_cr_str_buf_cat(str, ptr, len,
        rb_enc_to_index(ptr_enc), ENC_CODERANGE_UNKNOWN, NULL);
}

VALUE
rb_str_buf_cat_ascii(VALUE str, const char *ptr)
{
    /* ptr must reference NUL terminated ASCII string. */
    int encindex = ENCODING_GET(str);
    rb_encoding *enc = rb_enc_from_index(encindex);
    if (rb_enc_asciicompat(enc)) {
        return rb_enc_cr_str_buf_cat(str, ptr, strlen(ptr),
            encindex, ENC_CODERANGE_7BIT, 0);
    }
    else {
        char *buf = ALLOCA_N(char, rb_enc_mbmaxlen(enc));
        while (*ptr) {
            unsigned int c = (unsigned char)*ptr;
            int len = rb_enc_codelen(c, enc);
            rb_enc_mbcput(c, buf, enc);
            rb_enc_cr_str_buf_cat(str, buf, len,
                encindex, ENC_CODERANGE_VALID, 0);
            ptr++;
        }
        return str;
    }
}

VALUE
rb_str_buf_append(VALUE str, VALUE str2)
{
    int str2_cr;

    str2_cr = ENC_CODERANGE(str2);

    rb_enc_cr_str_buf_cat(str, RSTRING_PTR(str2), RSTRING_LEN(str2),
        ENCODING_GET(str2), str2_cr, &str2_cr);

    OBJ_INFECT(str, str2);
    ENC_CODERANGE_SET(str2, str2_cr);

    return str;
}

VALUE
rb_str_append(VALUE str, VALUE str2)
{
    rb_encoding *enc;
    int cr, cr2;
    long len2;

    StringValue(str2);
    if ((len2 = RSTRING_LEN(str2)) > 0 && STR_ASSOC_P(str)) {
        long len1 = RSTRING(str)->as.heap.len, len = len1 + len2;
        enc = rb_enc_check(str, str2);
        cr = ENC_CODERANGE(str);
        if ((cr2 = ENC_CODERANGE(str2)) > cr || RSTRING_LEN(str) == 0)
            cr = cr2;
        rb_str_modify_expand(str, len2);
        memcpy(RSTRING(str)->as.heap.ptr + len1, RSTRING_PTR(str2), len2);
        TERM_FILL(RSTRING(str)->as.heap.ptr + len, rb_enc_mbminlen(enc));
        RSTRING(str)->as.heap.len = len;
        rb_enc_associate(str, enc);
        ENC_CODERANGE_SET(str, cr);
        OBJ_INFECT(str, str2);
        return str;
    }
    return rb_str_buf_append(str, str2);
}

/*
 *  call-seq:
 *     str << integer       -> str
 *     str.concat(integer)  -> str
 *     str << obj           -> str
 *     str.concat(obj)      -> str
 *
 *  Append---Concatenates the given object to <i>str</i>. If the object is a
 *  <code>Integer</code>, it is considered as a codepoint, and is converted
 *  to a character before concatenation.
 *
 *     a = "hello "
 *     a << "world"   #=> "hello world"
 *     a.concat(33)   #=> "hello world!"
 */

VALUE
rb_str_concat(VALUE str1, VALUE str2)
{
    unsigned int code;
    rb_encoding *enc = STR_ENC_GET(str1);

    if (FIXNUM_P(str2) || RB_TYPE_P(str2, T_BIGNUM)) {
        if (rb_num_to_uint(str2, &code) == 0) {
        }
        else if (FIXNUM_P(str2)) {
            rb_raise(rb_eRangeError, "%ld out of char range", FIX2LONG(str2));
        }
        else {
            rb_raise(rb_eRangeError, "bignum out of char range");
        }
    }
    else {
        return rb_str_append(str1, str2);
    }

    if (enc == rb_usascii_encoding()) {
        /* US-ASCII automatically extended to ASCII-8BIT */
        char buf[1];
        buf[0] = (char)code;
        if (code > 0xFF) {
            rb_raise(rb_eRangeError, "%u out of char range", code);
        }
        rb_str_cat(str1, buf, 1);
        if (code > 127) {
            rb_enc_associate(str1, rb_ascii8bit_encoding());
            ENC_CODERANGE_SET(str1, ENC_CODERANGE_VALID);
        }
    }
    else {
        long pos = RSTRING_LEN(str1);
        int cr = ENC_CODERANGE(str1);
        int len;
        char *buf;

        switch (len = rb_enc_codelen(code, enc)) {
          case ONIGERR_INVALID_CODE_POINT_VALUE:
            rb_raise(rb_eRangeError, "invalid codepoint 0x%X in %s", code, rb_enc_name(enc));
            break;
          case ONIGERR_TOO_BIG_WIDE_CHAR_VALUE:
          case 0:
            rb_raise(rb_eRangeError, "%u out of char range", code);
            break;
        }
        buf = ALLOCA_N(char, len + 1);
        rb_enc_mbcput(code, buf, enc);
        if (rb_enc_precise_mbclen(buf, buf + len + 1, enc) != len) {
            rb_raise(rb_eRangeError, "invalid codepoint 0x%X in %s", code, rb_enc_name(enc));
        }
        rb_str_resize(str1, pos+len);
        memcpy(RSTRING_PTR(str1) + pos, buf, len);
        if (cr == ENC_CODERANGE_7BIT && code > 127)
            cr = ENC_CODERANGE_VALID;
        ENC_CODERANGE_SET(str1, cr);
    }
    return str1;
}

/*
 *  call-seq:
 *     str.prepend(other_str)  -> str
 *
 *  Prepend---Prepend the given string to <i>str</i>.
 *
 *     a = "world"
 *     a.prepend("hello ") #=> "hello world"
 *     a                   #=> "hello world"
 */

static VALUE
rb_str_prepend(VALUE str, VALUE str2)
{
    StringValue(str2);
    StringValue(str);
    rb_str_update(str, 0L, 0L, str2);
    return str;
}

st_index_t
rb_str_hash(VALUE str)
{
    int e = ENCODING_GET(str);
    if (e && rb_enc_str_coderange(str) == ENC_CODERANGE_7BIT) {
        e = 0;
    }
    return rb_memhash((const void *)RSTRING_PTR(str), RSTRING_LEN(str)) ^ e;
}

int
rb_str_hash_cmp(VALUE str1, VALUE str2)
{
    long len;

    if (!rb_str_comparable(str1, str2)) return 1;
    if (RSTRING_LEN(str1) == (len = RSTRING_LEN(str2)) &&
        memcmp(RSTRING_PTR(str1), RSTRING_PTR(str2), len) == 0) {
        return 0;
    }
    return 1;
}

/*
 * call-seq:
 *    str.hash   -> fixnum
 *
 * Return a hash based on the string's length and content.
 */

static VALUE
rb_str_hash_m(VALUE str)
{
    st_index_t hval = rb_str_hash(str);
    return INT2FIX(hval);
}

#define lesser(a,b) (((a)>(b))?(b):(a))

int
rb_str_comparable(VALUE str1, VALUE str2)
{
    int idx1, idx2;
    int rc1, rc2;

    if (RSTRING_LEN(str1) == 0) return TRUE;
    if (RSTRING_LEN(str2) == 0) return TRUE;
    idx1 = ENCODING_GET(str1);
    idx2 = ENCODING_GET(str2);
    if (idx1 == idx2) return TRUE;
    rc1 = rb_enc_str_coderange(str1);
    rc2 = rb_enc_str_coderange(str2);
    if (rc1 == ENC_CODERANGE_7BIT) {
        if (rc2 == ENC_CODERANGE_7BIT) return TRUE;
        if (rb_enc_asciicompat(rb_enc_from_index(idx2)))
            return TRUE;
    }
    if (rc2 == ENC_CODERANGE_7BIT) {
        if (rb_enc_asciicompat(rb_enc_from_index(idx1)))
            return TRUE;
    }
    return FALSE;
}

int
rb_str_cmp(VALUE str1, VALUE str2)
{
    long len1, len2;
    const char *ptr1, *ptr2;
    int retval;

    if (str1 == str2) return 0;
    RSTRING_GETMEM(str1, ptr1, len1);
    RSTRING_GETMEM(str2, ptr2, len2);
    if (ptr1 == ptr2 || (retval = memcmp(ptr1, ptr2, lesser(len1, len2))) == 0) {
        if (len1 == len2) {
            if (!rb_str_comparable(str1, str2)) {
                if (ENCODING_GET(str1) > ENCODING_GET(str2))
                    return 1;
                return -1;
            }
            return 0;
        }
        if (len1 > len2) return 1;
        return -1;
    }
    if (retval > 0) return 1;
    return -1;
}

/* expect tail call optimization */
static VALUE
str_eql(const VALUE str1, const VALUE str2)
{
    const long len = RSTRING_LEN(str1);
    const char *ptr1, *ptr2;

    if (len != RSTRING_LEN(str2)) return Qfalse;
    if (!rb_str_comparable(str1, str2)) return Qfalse;
    if ((ptr1 = RSTRING_PTR(str1)) == (ptr2 = RSTRING_PTR(str2)))
        return Qtrue;
    if (memcmp(ptr1, ptr2, len) == 0)
        return Qtrue;
    return Qfalse;
}

/*
 *  call-seq:
 *     str == obj    -> true or false
 *     str === obj   -> true or false
 *
 *  === Equality
 *
 *  Returns whether +str+ == +obj+, similar to Object#==.
 *
 *  If +obj+ is not an instance of String but responds to +to_str+, then the
 *  two strings are compared using case equality Object#===.
 *
 *  Otherwise, returns similarly to String#eql?, comparing length and content.
 */

VALUE
rb_str_equal(VALUE str1, VALUE str2)
{
    if (str1 == str2) return Qtrue;
    if (!RB_TYPE_P(str2, T_STRING)) {
        if (!rb_respond_to(str2, rb_intern("to_str"))) {
            return Qfalse;
        }
        return rb_equal(str2, str1);
    }
    return str_eql(str1, str2);
}

/*
 * call-seq:
 *   str.eql?(other)   -> true or false
 *
 * Two strings are equal if they have the same length and content.
 */

static VALUE
rb_str_eql(VALUE str1, VALUE str2)
{
    if (str1 == str2) return Qtrue;
    if (!RB_TYPE_P(str2, T_STRING)) return Qfalse;
    return str_eql(str1, str2);
}

/*
 *  call-seq:
 *     string <=> other_string   -> -1, 0, +1 or nil
 *
 *
 *  Comparison---Returns -1, 0, +1 or nil depending on whether +string+ is less
 *  than, equal to, or greater than +other_string+.
 *
 *  +nil+ is returned if the two values are incomparable.
 *
 *  If the strings are of different lengths, and the strings are equal when
 *  compared up to the shortest length, then the longer string is considered
 *  greater than the shorter one.
 *
 *  <code><=></code> is the basis for the methods <code><</code>,
 *  <code><=</code>, <code>></code>, <code>>=</code>, and
 *  <code>between?</code>, included from module Comparable. The method
 *  String#== does not use Comparable#==.
 *
 *     "abcdef" <=> "abcde"     #=> 1
 *     "abcdef" <=> "abcdef"    #=> 0
 *     "abcdef" <=> "abcdefg"   #=> -1
 *     "abcdef" <=> "ABCDEF"    #=> 1
 */

static VALUE
rb_str_cmp_m(VALUE str1, VALUE str2)
{
    int result;

    if (!RB_TYPE_P(str2, T_STRING)) {
        VALUE tmp = rb_check_funcall(str2, rb_intern("to_str"), 0, 0);
        if (RB_TYPE_P(tmp, T_STRING)) {
            result = rb_str_cmp(str1, tmp);
        }
        else {
            return rb_invcmp(str1, str2);
        }
    }
    else {
        result = rb_str_cmp(str1, str2);
    }
    return INT2FIX(result);
}

/*
 *  call-seq:
 *     str.casecmp(other_str)   -> -1, 0, +1 or nil
 *
 *  Case-insensitive version of <code>String#<=></code>.
 *
 *     "abcdef".casecmp("abcde")     #=> 1
 *     "aBcDeF".casecmp("abcdef")    #=> 0
 *     "abcdef".casecmp("abcdefg")   #=> -1
 *     "abcdef".casecmp("ABCDEF")    #=> 0
 */

static VALUE
rb_str_casecmp(VALUE str1, VALUE str2)
{
    long len;
    rb_encoding *enc;
    char *p1, *p1end, *p2, *p2end;

    StringValue(str2);
    enc = rb_enc_compatible(str1, str2);
    if (!enc) {
        return Qnil;
    }

    p1 = RSTRING_PTR(str1); p1end = RSTRING_END(str1);
    p2 = RSTRING_PTR(str2); p2end = RSTRING_END(str2);
    if (single_byte_optimizable(str1) && single_byte_optimizable(str2)) {
        while (p1 < p1end && p2 < p2end) {
            if (*p1 != *p2) {
                unsigned int c1 = TOUPPER(*p1 & 0xff);
                unsigned int c2 = TOUPPER(*p2 & 0xff);
                if (c1 != c2)
                    return INT2FIX(c1 < c2 ? -1 : 1);
            }
            p1++;
            p2++;
        }
    }
    else {
        while (p1 < p1end && p2 < p2end) {
            int l1, c1 = rb_enc_ascget(p1, p1end, &l1, enc);
            int l2, c2 = rb_enc_ascget(p2, p2end, &l2, enc);

            if (0 <= c1 && 0 <= c2) {
                c1 = TOUPPER(c1);
                c2 = TOUPPER(c2);
                if (c1 != c2)
                    return INT2FIX(c1 < c2 ? -1 : 1);
            }
            else {
                int r;
                l1 = rb_enc_mbclen(p1, p1end, enc);
                l2 = rb_enc_mbclen(p2, p2end, enc);
                len = l1 < l2 ? l1 : l2;
                r = memcmp(p1, p2, len);
                if (r != 0)
                    return INT2FIX(r < 0 ? -1 : 1);
                if (l1 != l2)
                    return INT2FIX(l1 < l2 ? -1 : 1);
            }
            p1 += l1;
            p2 += l2;
        }
    }
    if (RSTRING_LEN(str1) == RSTRING_LEN(str2)) return INT2FIX(0);
    if (RSTRING_LEN(str1) > RSTRING_LEN(str2)) return INT2FIX(1);
    return INT2FIX(-1);
}

static long
rb_str_index(VALUE str, VALUE sub, long offset)
{
    char *s, *sptr, *e;
    long pos, len, slen;
    int single_byte = single_byte_optimizable(str);
    rb_encoding *enc;

    enc = rb_enc_check(str, sub);
    if (is_broken_string(sub)) return -1;

    len = single_byte ? RSTRING_LEN(str) : str_strlen(str, enc);
    slen = str_strlen(sub, enc);
    if (offset < 0) {
        offset += len;
        if (offset < 0) return -1;
    }
    if (len - offset < slen) return -1;

    s = RSTRING_PTR(str);
    e = RSTRING_END(str);
    if (offset) {
        offset = str_offset(s, e, offset, enc, single_byte);
        s += offset;
    }
    if (slen == 0) return offset;
    /* need proceed one character at a time */
    sptr = RSTRING_PTR(sub);
    slen = RSTRING_LEN(sub);
    len = RSTRING_LEN(str) - offset;
    for (;;) {
        char *t;
        pos = rb_memsearch(sptr, slen, s, len, enc);
        if (pos < 0) return pos;
        t = rb_enc_right_char_head(s, s+pos, e, enc);
        if (t == s + pos) break;
        len -= t - s;
        if (len <= 0) return -1;
        offset += t - s;
        s = t;
    }
    return pos + offset;
}


/*
 *  call-seq:
 *     str.index(substring [, offset])   -> fixnum or nil
 *     str.index(regexp [, offset])      -> fixnum or nil
 *
 *  Returns the index of the first occurrence of the given <i>substring</i> or
 *  pattern (<i>regexp</i>) in <i>str</i>. Returns <code>nil</code> if not
 *  found. If the second parameter is present, it specifies the position in the
 *  string to begin the search.
 *
 *     "hello".index('e')             #=> 1
 *     "hello".index('lo')            #=> 3
 *     "hello".index('a')             #=> nil
 *     "hello".index(?e)              #=> 1
 *     "hello".index(/[aeiou]/, -3)   #=> 4
 */

static VALUE
rb_str_index_m(int argc, VALUE *argv, VALUE str)
{
    VALUE sub;
    VALUE initpos;
    long pos;

    if (rb_scan_args(argc, argv, "11", &sub, &initpos) == 2) {
        pos = NUM2LONG(initpos);
    }
    else {
        pos = 0;
    }
    if (pos < 0) {
        pos += str_strlen(str, STR_ENC_GET(str));
        if (pos < 0) {
            if (RB_TYPE_P(sub, T_REGEXP)) {
                rb_backref_set(Qnil);
            }
            return Qnil;
        }
    }

    if (SPECIAL_CONST_P(sub)) goto generic;
    switch (BUILTIN_TYPE(sub)) {
      case T_REGEXP:
        if (pos > str_strlen(str, STR_ENC_GET(str)))
            return Qnil;
        pos = str_offset(RSTRING_PTR(str), RSTRING_END(str), pos,
                         rb_enc_check(str, sub), single_byte_optimizable(str));

        pos = rb_reg_search(sub, str, pos, 0);
        pos = rb_str_sublen(str, pos);
        break;

      generic:
      default: {
        VALUE tmp;

        tmp = rb_check_string_type(sub);
        if (NIL_P(tmp)) {
            rb_raise(rb_eTypeError, "type mismatch: %s given",
                     rb_obj_classname(sub));
        }
        sub = tmp;
      }
        /* fall through */
      case T_STRING:
        pos = rb_str_index(str, sub, pos);
        pos = rb_str_sublen(str, pos);
        break;
    }

    if (pos == -1) return Qnil;
    return LONG2NUM(pos);
}

#ifdef HAVE_MEMRCHR
static long
str_rindex(VALUE str, VALUE sub, const char *s, long pos, rb_encoding *enc)
{
    char *hit, *adjusted;
    int c;
    long slen, searchlen;
    char *sbeg, *e, *t;

    slen = RSTRING_LEN(sub);
    if (slen == 0) return pos;
    sbeg = RSTRING_PTR(str);
    e = RSTRING_END(str);
    t = RSTRING_PTR(sub);
    c = *t & 0xff;
    searchlen = s - sbeg + 1;

    do {
        hit = memrchr(sbeg, c, searchlen);
        if (!hit) break;
        adjusted = rb_enc_left_char_head(sbeg, hit, e, enc);
        if (hit != adjusted) {
            searchlen = adjusted - sbeg;
            continue;
        }
        if (memcmp(hit, t, slen) == 0)
            return rb_str_sublen(str, hit - sbeg);
        searchlen = adjusted - sbeg;
    } while (searchlen > 0);

    return -1;
}
#else
static long
str_rindex(VALUE str, VALUE sub, const char *s, long pos, rb_encoding *enc)
{
    long slen;
    char *sbeg, *e, *t;

    sbeg = RSTRING_PTR(str);
    e = RSTRING_END(str);
    t = RSTRING_PTR(sub);
    slen = RSTRING_LEN(sub);

    while (s) {
        if (memcmp(s, t, slen) == 0) {
            return pos;
        }
        if (pos == 0) break;
        pos--;
        s = rb_enc_prev_char(sbeg, s, e, enc);
    }

    return -1;
}
#endif

static long
rb_str_rindex(VALUE str, VALUE sub, long pos)
{
    long len, slen;
    char *sbeg, *s;
    rb_encoding *enc;
    int singlebyte;

    enc = rb_enc_check(str, sub);
    if (is_broken_string(sub)) return -1;
    singlebyte = single_byte_optimizable(str);
    len = singlebyte ? RSTRING_LEN(str) : str_strlen(str, enc);
    slen = str_strlen(sub, enc);

    /* substring longer than string */
    if (len < slen) return -1;
    if (len - pos < slen) pos = len - slen;
    if (len == 0) return pos;

    sbeg = RSTRING_PTR(str);

    if (pos == 0) {
        if (memcmp(sbeg, RSTRING_PTR(sub), RSTRING_LEN(sub)) == 0)
            return 0;
        else
            return -1;
    }

    s = str_nth(sbeg, RSTRING_END(str), pos, enc, singlebyte);
    return str_rindex(str, sub, s, pos, enc);
}


/*
 *  call-seq:
 *     str.rindex(substring [, fixnum])   -> fixnum or nil
 *     str.rindex(regexp [, fixnum])   -> fixnum or nil
 *
 *  Returns the index of the last occurrence of the given <i>substring</i> or
 *  pattern (<i>regexp</i>) in <i>str</i>. Returns <code>nil</code> if not
 *  found. If the second parameter is present, it specifies the position in the
 *  string to end the search---characters beyond this point will not be
 *  considered.
 *
 *     "hello".rindex('e')             #=> 1
 *     "hello".rindex('l')             #=> 3
 *     "hello".rindex('a')             #=> nil
 *     "hello".rindex(?e)              #=> 1
 *     "hello".rindex(/[aeiou]/, -2)   #=> 1
 */

static VALUE
rb_str_rindex_m(int argc, VALUE *argv, VALUE str)
{
    VALUE sub;
    VALUE vpos;
    rb_encoding *enc = STR_ENC_GET(str);
    long pos, len = str_strlen(str, enc);

    if (rb_scan_args(argc, argv, "11", &sub, &vpos) == 2) {
        pos = NUM2LONG(vpos);
        if (pos < 0) {
            pos += len;
            if (pos < 0) {
                if (RB_TYPE_P(sub, T_REGEXP)) {
                    rb_backref_set(Qnil);
                }
                return Qnil;
            }
        }
        if (pos > len) pos = len;
    }
    else {
        pos = len;
    }

    if (SPECIAL_CONST_P(sub)) goto generic;
    switch (BUILTIN_TYPE(sub)) {
      case T_REGEXP:
        /* enc = rb_get_check(str, sub); */
        pos = str_offset(RSTRING_PTR(str), RSTRING_END(str), pos,
                         STR_ENC_GET(str), single_byte_optimizable(str));

        if (!RREGEXP(sub)->ptr || RREGEXP_SRC_LEN(sub)) {
            pos = rb_reg_search(sub, str, pos, 1);
            pos = rb_str_sublen(str, pos);
        }
        if (pos >= 0) return LONG2NUM(pos);
        break;

      generic:
      default: {
        VALUE tmp;

        tmp = rb_check_string_type(sub);
        if (NIL_P(tmp)) {
            rb_raise(rb_eTypeError, "type mismatch: %s given",
                     rb_obj_classname(sub));
        }
        sub = tmp;
      }
        /* fall through */
      case T_STRING:
        pos = rb_str_rindex(str, sub, pos);
        if (pos >= 0) return LONG2NUM(pos);
        break;
    }
    return Qnil;
}

/*
 *  call-seq:
 *     str =~ obj   -> fixnum or nil
 *
 *  Match---If <i>obj</i> is a <code>Regexp</code>, use it as a pattern to match
 *  against <i>str</i>,and returns the position the match starts, or
 *  <code>nil</code> if there is no match. Otherwise, invokes
 *  <i>obj.=~</i>, passing <i>str</i> as an argument. The default
 *  <code>=~</code> in <code>Object</code> returns <code>nil</code>.
 *
 *  Note: <code>str =~ regexp</code> is not the same as
 *  <code>regexp =~ str</code>. Strings captured from named capture groups
 *  are assigned to local variables only in the second case.
 *
 *     "cat o' 9 tails" =~ /\d/   #=> 7
 *     "cat o' 9 tails" =~ 9      #=> nil
 */

static VALUE
rb_str_match(VALUE x, VALUE y)
{
    if (SPECIAL_CONST_P(y)) goto generic;
    switch (BUILTIN_TYPE(y)) {
      case T_STRING:
        rb_raise(rb_eTypeError, "type mismatch: String given");

      case T_REGEXP:
        return rb_reg_match(y, x);

      generic:
      default:
        return rb_funcall(y, rb_intern("=~"), 1, x);
    }
}


static VALUE get_pat(VALUE, int);


/*
 *  call-seq:
 *     str.match(pattern)        -> matchdata or nil
 *     str.match(pattern, pos)   -> matchdata or nil
 *
 *  Converts <i>pattern</i> to a <code>Regexp</code> (if it isn't already one),
 *  then invokes its <code>match</code> method on <i>str</i>.  If the second
 *  parameter is present, it specifies the position in the string to begin the
 *  search.
 *
 *     'hello'.match('(.)\1')      #=> #<MatchData "ll" 1:"l">
 *     'hello'.match('(.)\1')[0]   #=> "ll"
 *     'hello'.match(/(.)\1/)[0]   #=> "ll"
 *     'hello'.match('xx')         #=> nil
 *
 *  If a block is given, invoke the block with MatchData if match succeed, so
 *  that you can write
 *
 *     str.match(pat) {|m| ...}
 *
 *  instead of
 *
 *     if m = str.match(pat)
 *       ...
 *     end
 *
 *  The return value is a value from block execution in this case.
 */

static VALUE
rb_str_match_m(int argc, VALUE *argv, VALUE str)
{
    VALUE re, result;
    if (argc < 1)
        rb_check_arity(argc, 1, 2);
    re = argv[0];
    argv[0] = str;
    result = rb_funcall2(get_pat(re, 0), rb_intern("match"), argc, argv);
    if (!NIL_P(result) && rb_block_given_p()) {
        return rb_yield(result);
    }
    return result;
}

enum neighbor_char {
    NEIGHBOR_NOT_CHAR,
    NEIGHBOR_FOUND,
    NEIGHBOR_WRAPPED
};

static enum neighbor_char
enc_succ_char(char *p, long len, rb_encoding *enc)
{
    long i;
    int l;

    if (rb_enc_mbminlen(enc) > 1) {
        /* wchar, trivial case */
        int r = rb_enc_precise_mbclen(p, p + len, enc), c;
        if (!MBCLEN_CHARFOUND_P(r)) {
            return NEIGHBOR_NOT_CHAR;
        }
        c = rb_enc_mbc_to_codepoint(p, p + len, enc) + 1;
        l = rb_enc_code_to_mbclen(c, enc);
        if (!l) return NEIGHBOR_NOT_CHAR;
        if (l != len) return NEIGHBOR_WRAPPED;
        rb_enc_mbcput(c, p, enc);
        r = rb_enc_precise_mbclen(p, p + len, enc);
        if (!MBCLEN_CHARFOUND_P(r)) {
            return NEIGHBOR_NOT_CHAR;
        }
        return NEIGHBOR_FOUND;
    }
    while (1) {
        for (i = len-1; 0 <= i && (unsigned char)p[i] == 0xff; i--)
            p[i] = '\0';
        if (i < 0)
            return NEIGHBOR_WRAPPED;
        ++((unsigned char*)p)[i];
        l = rb_enc_precise_mbclen(p, p+len, enc);
        if (MBCLEN_CHARFOUND_P(l)) {
            l = MBCLEN_CHARFOUND_LEN(l);
            if (l == len) {
                return NEIGHBOR_FOUND;
            }
            else {
                memset(p+l, 0xff, len-l);
            }
        }
        if (MBCLEN_INVALID_P(l) && i < len-1) {
            long len2;
            int l2;
            for (len2 = len-1; 0 < len2; len2--) {
                l2 = rb_enc_precise_mbclen(p, p+len2, enc);
                if (!MBCLEN_INVALID_P(l2))
                    break;
            }
            memset(p+len2+1, 0xff, len-(len2+1));
        }
    }
}

static enum neighbor_char
enc_pred_char(char *p, long len, rb_encoding *enc)
{
    long i;
    int l;
    if (rb_enc_mbminlen(enc) > 1) {
        /* wchar, trivial case */
        int r = rb_enc_precise_mbclen(p, p + len, enc), c;
        if (!MBCLEN_CHARFOUND_P(r)) {
            return NEIGHBOR_NOT_CHAR;
        }
        c = rb_enc_mbc_to_codepoint(p, p + len, enc);
        if (!c) return NEIGHBOR_NOT_CHAR;
        --c;
        l = rb_enc_code_to_mbclen(c, enc);
        if (!l) return NEIGHBOR_NOT_CHAR;
        if (l != len) return NEIGHBOR_WRAPPED;
        rb_enc_mbcput(c, p, enc);
        r = rb_enc_precise_mbclen(p, p + len, enc);
        if (!MBCLEN_CHARFOUND_P(r)) {
            return NEIGHBOR_NOT_CHAR;
        }
        return NEIGHBOR_FOUND;
    }
    while (1) {
        for (i = len-1; 0 <= i && (unsigned char)p[i] == 0; i--)
            p[i] = '\xff';
        if (i < 0)
            return NEIGHBOR_WRAPPED;
        --((unsigned char*)p)[i];
        l = rb_enc_precise_mbclen(p, p+len, enc);
        if (MBCLEN_CHARFOUND_P(l)) {
            l = MBCLEN_CHARFOUND_LEN(l);
            if (l == len) {
                return NEIGHBOR_FOUND;
            }
            else {
                memset(p+l, 0, len-l);
            }
        }
        if (MBCLEN_INVALID_P(l) && i < len-1) {
            long len2;
            int l2;
            for (len2 = len-1; 0 < len2; len2--) {
                l2 = rb_enc_precise_mbclen(p, p+len2, enc);
                if (!MBCLEN_INVALID_P(l2))
                    break;
            }
            memset(p+len2+1, 0, len-(len2+1));
        }
    }
}

/*
  overwrite +p+ by succeeding letter in +enc+ and returns
  NEIGHBOR_FOUND or NEIGHBOR_WRAPPED.
  When NEIGHBOR_WRAPPED, carried-out letter is stored into carry.
  assuming each ranges are successive, and mbclen
  never change in each ranges.
  NEIGHBOR_NOT_CHAR is returned if invalid character or the range has only one
  character.
 */
static enum neighbor_char
enc_succ_alnum_char(char *p, long len, rb_encoding *enc, char *carry)
{
    enum neighbor_char ret;
    unsigned int c;
    int ctype;
    int range;
    char save[ONIGENC_CODE_TO_MBC_MAXLEN];

    /* skip 03A2, invalid char between GREEK CAPITAL LETTERS */
    int try;
    const int max_gaps = 1;

    c = rb_enc_mbc_to_codepoint(p, p+len, enc);
    if (rb_enc_isctype(c, ONIGENC_CTYPE_DIGIT, enc))
        ctype = ONIGENC_CTYPE_DIGIT;
    else if (rb_enc_isctype(c, ONIGENC_CTYPE_ALPHA, enc))
        ctype = ONIGENC_CTYPE_ALPHA;
    else
        return NEIGHBOR_NOT_CHAR;

    MEMCPY(save, p, char, len);
    for (try = 0; try <= max_gaps; ++try) {
        ret = enc_succ_char(p, len, enc);
        if (ret == NEIGHBOR_FOUND) {
            c = rb_enc_mbc_to_codepoint(p, p+len, enc);
            if (rb_enc_isctype(c, ctype, enc))
                return NEIGHBOR_FOUND;
        }
    }
    MEMCPY(p, save, char, len);
    range = 1;
    while (1) {
        MEMCPY(save, p, char, len);
        ret = enc_pred_char(p, len, enc);
        if (ret == NEIGHBOR_FOUND) {
            c = rb_enc_mbc_to_codepoint(p, p+len, enc);
            if (!rb_enc_isctype(c, ctype, enc)) {
                MEMCPY(p, save, char, len);
                break;
            }
        }
        else {
            MEMCPY(p, save, char, len);
            break;
        }
        range++;
    }
    if (range == 1) {
        return NEIGHBOR_NOT_CHAR;
    }

    if (ctype != ONIGENC_CTYPE_DIGIT) {
        MEMCPY(carry, p, char, len);
        return NEIGHBOR_WRAPPED;
    }

    MEMCPY(carry, p, char, len);
    enc_succ_char(carry, len, enc);
    return NEIGHBOR_WRAPPED;
}


/*
 *  call-seq:
 *     str.succ   -> new_str
 *     str.next   -> new_str
 *
 *  Returns the successor to <i>str</i>. The successor is calculated by
 *  incrementing characters starting from the rightmost alphanumeric (or
 *  the rightmost character if there are no alphanumerics) in the
 *  string. Incrementing a digit always results in another digit, and
 *  incrementing a letter results in another letter of the same case.
 *  Incrementing nonalphanumerics uses the underlying character set's
 *  collating sequence.
 *
 *  If the increment generates a ``carry,'' the character to the left of
 *  it is incremented. This process repeats until there is no carry,
 *  adding an additional character if necessary.
 *
 *     "abcd".succ        #=> "abce"
 *     "THX1138".succ     #=> "THX1139"
 *     "<<koala>>".succ   #=> "<<koalb>>"
 *     "1999zzz".succ     #=> "2000aaa"
 *     "ZZZ9999".succ     #=> "AAAA0000"
 *     "***".succ         #=> "**+"
 */

VALUE
rb_str_succ(VALUE orig)
{
    rb_encoding *enc;
    VALUE str;
    char *sbeg, *s, *e, *last_alnum = 0;
    int c = -1;
    long l;
    char carry[ONIGENC_CODE_TO_MBC_MAXLEN] = "\1";
    long carry_pos = 0, carry_len = 1;
    enum neighbor_char neighbor = NEIGHBOR_FOUND;

    str = rb_str_new5(orig, RSTRING_PTR(orig), RSTRING_LEN(orig));
    rb_enc_cr_str_copy_for_substr(str, orig);
    OBJ_INFECT(str, orig);
    if (RSTRING_LEN(str) == 0) return str;

    enc = STR_ENC_GET(orig);
    sbeg = RSTRING_PTR(str);
    s = e = sbeg + RSTRING_LEN(str);

    while ((s = rb_enc_prev_char(sbeg, s, e, enc)) != 0) {
        if (neighbor == NEIGHBOR_NOT_CHAR && last_alnum) {
            if (ISALPHA(*last_alnum) ? ISDIGIT(*s) :
                ISDIGIT(*last_alnum) ? ISALPHA(*s) : 0) {
                s = last_alnum;
                break;
            }
        }
        l = rb_enc_precise_mbclen(s, e, enc);
        if (!ONIGENC_MBCLEN_CHARFOUND_P(l)) continue;
        l = ONIGENC_MBCLEN_CHARFOUND_LEN(l);
        neighbor = enc_succ_alnum_char(s, l, enc, carry);
        switch (neighbor) {
          case NEIGHBOR_NOT_CHAR:
            continue;
          case NEIGHBOR_FOUND:
            return str;
          case NEIGHBOR_WRAPPED:
            last_alnum = s;
            break;
        }
        c = 1;
        carry_pos = s - sbeg;
        carry_len = l;
    }
    if (c == -1) {              /* str contains no alnum */
        s = e;
        while ((s = rb_enc_prev_char(sbeg, s, e, enc)) != 0) {
            enum neighbor_char neighbor;
            char tmp[ONIGENC_CODE_TO_MBC_MAXLEN];
            l = rb_enc_precise_mbclen(s, e, enc);
            if (!ONIGENC_MBCLEN_CHARFOUND_P(l)) continue;
            l = ONIGENC_MBCLEN_CHARFOUND_LEN(l);
            MEMCPY(tmp, s, char, l);
            neighbor = enc_succ_char(tmp, l, enc);
            switch (neighbor) {
              case NEIGHBOR_FOUND:
                MEMCPY(s, tmp, char, l);
                return str;
                break;
              case NEIGHBOR_WRAPPED:
                MEMCPY(s, tmp, char, l);
                break;
              case NEIGHBOR_NOT_CHAR:
                break;
            }
            if (rb_enc_precise_mbclen(s, s+l, enc) != l) {
                /* wrapped to \0...\0.  search next valid char. */
                enc_succ_char(s, l, enc);
            }
            if (!rb_enc_asciicompat(enc)) {
                MEMCPY(carry, s, char, l);
                carry_len = l;
            }
            carry_pos = s - sbeg;
        }
    }
    RESIZE_CAPA(str, RSTRING_LEN(str) + carry_len);
    s = RSTRING_PTR(str) + carry_pos;
    memmove(s + carry_len, s, RSTRING_LEN(str) - carry_pos);
    memmove(s, carry, carry_len);
    STR_SET_LEN(str, RSTRING_LEN(str) + carry_len);
    RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';
    rb_enc_str_coderange(str);
    return str;
}


/*
 *  call-seq:
 *     str.succ!   -> str
 *     str.next!   -> str
 *
 *  Equivalent to <code>String#succ</code>, but modifies the receiver in
 *  place.
 */

static VALUE
rb_str_succ_bang(VALUE str)
{
    rb_str_shared_replace(str, rb_str_succ(str));

    return str;
}


/*
 *  call-seq:
 *     str.upto(other_str, exclusive=false) {|s| block }   -> str
 *     str.upto(other_str, exclusive=false)                -> an_enumerator
 *
 *  Iterates through successive values, starting at <i>str</i> and
 *  ending at <i>other_str</i> inclusive, passing each value in turn to
 *  the block. The <code>String#succ</code> method is used to generate
 *  each value.  If optional second argument exclusive is omitted or is false,
 *  the last value will be included; otherwise it will be excluded.
 *
 *  If no block is given, an enumerator is returned instead.
 *
 *     "a8".upto("b6") {|s| print s, ' ' }
 *     for s in "a8".."b6"
 *       print s, ' '
 *     end
 *
 *  <em>produces:</em>
 *
 *     a8 a9 b0 b1 b2 b3 b4 b5 b6
 *     a8 a9 b0 b1 b2 b3 b4 b5 b6
 *
 *  If <i>str</i> and <i>other_str</i> contains only ascii numeric characters,
 *  both are recognized as decimal numbers. In addition, the width of
 *  string (e.g. leading zeros) is handled appropriately.
 *
 *     "9".upto("11").to_a   #=> ["9", "10", "11"]
 *     "25".upto("5").to_a   #=> []
 *     "07".upto("11").to_a  #=> ["07", "08", "09", "10", "11"]
 */

static VALUE
rb_str_upto(int argc, VALUE *argv, VALUE beg)
{
    VALUE end, exclusive;
    VALUE current, after_end;
    ID succ;
    int n, excl, ascii;
    rb_encoding *enc;

    rb_scan_args(argc, argv, "11", &end, &exclusive);
    RETURN_ENUMERATOR(beg, argc, argv);
    excl = RTEST(exclusive);
    CONST_ID(succ, "succ");
    StringValue(end);
    enc = rb_enc_check(beg, end);
    ascii = (is_ascii_string(beg) && is_ascii_string(end));
    /* single character */
    if (RSTRING_LEN(beg) == 1 && RSTRING_LEN(end) == 1 && ascii) {
        char c = RSTRING_PTR(beg)[0];
        char e = RSTRING_PTR(end)[0];

        if (c > e || (excl && c == e)) return beg;
        for (;;) {
            rb_yield(rb_enc_str_new(&c, 1, enc));
            if (!excl && c == e) break;
            c++;
            if (excl && c == e) break;
        }
        return beg;
    }
    /* both edges are all digits */
    if (ascii && ISDIGIT(RSTRING_PTR(beg)[0]) && ISDIGIT(RSTRING_PTR(end)[0])) {
        char *s, *send;
        VALUE b, e;
        int width;

        s = RSTRING_PTR(beg); send = RSTRING_END(beg);
        width = rb_long2int(send - s);
        while (s < send) {
            if (!ISDIGIT(*s)) goto no_digits;
            s++;
        }
        s = RSTRING_PTR(end); send = RSTRING_END(end);
        while (s < send) {
            if (!ISDIGIT(*s)) goto no_digits;
            s++;
        }
        b = rb_str_to_inum(beg, 10, FALSE);
        e = rb_str_to_inum(end, 10, FALSE);
        if (FIXNUM_P(b) && FIXNUM_P(e)) {
            long bi = FIX2LONG(b);
            long ei = FIX2LONG(e);
            rb_encoding *usascii = rb_usascii_encoding();

            while (bi <= ei) {
                if (excl && bi == ei) break;
                rb_yield(rb_enc_sprintf(usascii, "%.*ld", width, bi));
                bi++;
            }
        }
        else {
            ID op = excl ? '<' : rb_intern("<=");
            VALUE args[2], fmt = rb_obj_freeze(rb_usascii_str_new_cstr("%.*d"));

            args[0] = INT2FIX(width);
            while (rb_funcall(b, op, 1, e)) {
                args[1] = b;
                rb_yield(rb_str_format(numberof(args), args, fmt));
                b = rb_funcall(b, succ, 0, 0);
            }
        }
        return beg;
    }
    /* normal case */
  no_digits:
    n = rb_str_cmp(beg, end);
    if (n > 0 || (excl && n == 0)) return beg;

    after_end = rb_funcall(end, succ, 0, 0);
    current = rb_str_dup(beg);
    while (!rb_str_equal(current, after_end)) {
        VALUE next = Qnil;
        if (excl || !rb_str_equal(current, end))
            next = rb_funcall(current, succ, 0, 0);
        rb_yield(current);
        if (NIL_P(next)) break;
        current = next;
        StringValue(current);
        if (excl && rb_str_equal(current, end)) break;
        if (RSTRING_LEN(current) > RSTRING_LEN(end) || RSTRING_LEN(current) == 0)
            break;
    }

    return beg;
}

static VALUE
rb_str_subpat(VALUE str, VALUE re, VALUE backref)
{
    if (rb_reg_search(re, str, 0, 0) >= 0) {
        VALUE match = rb_backref_get();
        int nth = rb_reg_backref_number(match, backref);
        return rb_reg_nth_match(nth, match);
    }
    return Qnil;
}

static VALUE
rb_str_aref(VALUE str, VALUE indx)
{
    long idx;

    if (FIXNUM_P(indx)) {
        idx = FIX2LONG(indx);

      num_index:
        str = rb_str_substr(str, idx, 1);
        if (!NIL_P(str) && RSTRING_LEN(str) == 0) return Qnil;
        return str;
    }

    if (SPECIAL_CONST_P(indx)) goto generic;
    switch (BUILTIN_TYPE(indx)) {
      case T_REGEXP:
        return rb_str_subpat(str, indx, INT2FIX(0));

      case T_STRING:
        if (rb_str_index(str, indx, 0) != -1)
            return rb_str_dup(indx);
        return Qnil;

      generic:
      default:
        /* check if indx is Range */
        {
            long beg, len;
            VALUE tmp;

            len = str_strlen(str, STR_ENC_GET(str));
            switch (rb_range_beg_len(indx, &beg, &len, len, 0)) {
              case Qfalse:
                break;
              case Qnil:
                return Qnil;
              default:
                tmp = rb_str_substr(str, beg, len);
                return tmp;
            }
        }
        idx = NUM2LONG(indx);
        goto num_index;
    }

    UNREACHABLE;
}


/*
 *  call-seq:
 *     str[index]                 -> new_str or nil
 *     str[start, length]         -> new_str or nil
 *     str[range]                 -> new_str or nil
 *     str[regexp]                -> new_str or nil
 *     str[regexp, capture]       -> new_str or nil
 *     str[match_str]             -> new_str or nil
 *     str.slice(index)           -> new_str or nil
 *     str.slice(start, length)   -> new_str or nil
 *     str.slice(range)           -> new_str or nil
 *     str.slice(regexp)          -> new_str or nil
 *     str.slice(regexp, capture) -> new_str or nil
 *     str.slice(match_str)       -> new_str or nil
 *
 *  Element Reference --- If passed a single +index+, returns a substring of
 *  one character at that index. If passed a +start+ index and a +length+,
 *  returns a substring containing +length+ characters starting at the
 *  +index+. If passed a +range+, its beginning and end are interpreted as
 *  offsets delimiting the substring to be returned.
 *
 *  In these three cases, if an index is negative, it is counted from the end
 *  of the string.  For the +start+ and +range+ cases the starting index
 *  is just before a character and an index matching the string's size.
 *  Additionally, an empty string is returned when the starting index for a
 *  character range is at the end of the string.
 *
 *  Returns +nil+ if the initial index falls outside the string or the length
 *  is negative.
 *
 *  If a +Regexp+ is supplied, the matching portion of the string is
 *  returned.  If a +capture+ follows the regular expression, which may be a
 *  capture group index or name, follows the regular expression that component
 *  of the MatchData is returned instead.
 *
 *  If a +match_str+ is given, that string is returned if it occurs in
 *  the string.
 *
 *  Returns +nil+ if the regular expression does not match or the match string
 *  cannot be found.
 *
 *     a = "hello there"
 *
 *     a[1]                   #=> "e"
 *     a[2, 3]                #=> "llo"
 *     a[2..3]                #=> "ll"
 *
 *     a[-3, 2]               #=> "er"
 *     a[7..-2]               #=> "her"
 *     a[-4..-2]              #=> "her"
 *     a[-2..-4]              #=> ""
 *
 *     a[11, 0]               #=> ""
 *     a[11]                  #=> nil
 *     a[12, 0]               #=> nil
 *     a[12..-1]              #=> nil
 *
 *     a[/[aeiou](.)\1/]      #=> "ell"
 *     a[/[aeiou](.)\1/, 0]   #=> "ell"
 *     a[/[aeiou](.)\1/, 1]   #=> "l"
 *     a[/[aeiou](.)\1/, 2]   #=> nil
 *
 *     a[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] #=> "l"
 *     a[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "vowel"]     #=> "e"
 *
 *     a["lo"]                #=> "lo"
 *     a["bye"]               #=> nil
 */

static VALUE
rb_str_aref_m(int argc, VALUE *argv, VALUE str)
{
    if (argc == 2) {
        if (RB_TYPE_P(argv[0], T_REGEXP)) {
            return rb_str_subpat(str, argv[0], argv[1]);
        }
        return rb_str_substr(str, NUM2LONG(argv[0]), NUM2LONG(argv[1]));
    }
    rb_check_arity(argc, 1, 2);
    return rb_str_aref(str, argv[0]);
}

VALUE
rb_str_drop_bytes(VALUE str, long len)
{
    char *ptr = RSTRING_PTR(str);
    long olen = RSTRING_LEN(str), nlen;

    str_modifiable(str);
    if (len > olen) len = olen;
    nlen = olen - len;
    if (nlen <= RSTRING_EMBED_LEN_MAX) {
        char *oldptr = ptr;
        int fl = (int)(RBASIC(str)->flags & (STR_NOEMBED|ELTS_SHARED));
        STR_SET_EMBED(str);
        STR_SET_EMBED_LEN(str, nlen);
        ptr = RSTRING(str)->as.ary;
        memmove(ptr, oldptr + len, nlen);
        if (fl == STR_NOEMBED) xfree(oldptr);
    }
    else {
        if (!STR_SHARED_P(str)) rb_str_new4(str);
        ptr = RSTRING(str)->as.heap.ptr += len;
        RSTRING(str)->as.heap.len = nlen;
    }
    ptr[nlen] = 0;
    ENC_CODERANGE_CLEAR(str);
    return str;
}

static void
rb_str_splice_0(VALUE str, long beg, long len, VALUE val)
{
    if (beg == 0 && RSTRING_LEN(val) == 0) {
        rb_str_drop_bytes(str, len);
        OBJ_INFECT(str, val);
        return;
    }

    rb_str_modify(str);
    if (len < RSTRING_LEN(val)) {
        /* expand string */
        RESIZE_CAPA(str, RSTRING_LEN(str) + RSTRING_LEN(val) - len + TERM_LEN(str));
    }

    if (RSTRING_LEN(val) != len) {
        memmove(RSTRING_PTR(str) + beg + RSTRING_LEN(val),
                RSTRING_PTR(str) + beg + len,
                RSTRING_LEN(str) - (beg + len));
    }
    if (RSTRING_LEN(val) < beg && len < 0) {
        MEMZERO(RSTRING_PTR(str) + RSTRING_LEN(str), char, -len);
    }
    if (RSTRING_LEN(val) > 0) {
        memmove(RSTRING_PTR(str)+beg, RSTRING_PTR(val), RSTRING_LEN(val));
    }
    STR_SET_LEN(str, RSTRING_LEN(str) + RSTRING_LEN(val) - len);
    if (RSTRING_PTR(str)) {
        RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';
    }
    OBJ_INFECT(str, val);
}

static void
rb_str_splice(VALUE str, long beg, long len, VALUE val)
{
    long slen;
    char *p, *e;
    rb_encoding *enc;
    int singlebyte = single_byte_optimizable(str);
    int cr;

    if (len < 0) rb_raise(rb_eIndexError, "negative length %ld", len);

    StringValue(val);
    enc = rb_enc_check(str, val);
    slen = str_strlen(str, enc);

    if (slen < beg) {
      out_of_range:
        rb_raise(rb_eIndexError, "index %ld out of string", beg);
    }
    if (beg < 0) {
        if (-beg > slen) {
            goto out_of_range;
        }
        beg += slen;
    }
    if (slen < len || slen < beg + len) {
        len = slen - beg;
    }
    str_modify_keep_cr(str);
    p = str_nth(RSTRING_PTR(str), RSTRING_END(str), beg, enc, singlebyte);
    if (!p) p = RSTRING_END(str);
    e = str_nth(p, RSTRING_END(str), len, enc, singlebyte);
    if (!e) e = RSTRING_END(str);
    /* error check */
    beg = p - RSTRING_PTR(str); /* physical position */
    len = e - p;                /* physical length */
    rb_str_splice_0(str, beg, len, val);
    rb_enc_associate(str, enc);
    cr = ENC_CODERANGE_AND(ENC_CODERANGE(str), ENC_CODERANGE(val));
    if (cr != ENC_CODERANGE_BROKEN)
        ENC_CODERANGE_SET(str, cr);
}

void
rb_str_update(VALUE str, long beg, long len, VALUE val)
{
    rb_str_splice(str, beg, len, val);
}

static void
rb_str_subpat_set(VALUE str, VALUE re, VALUE backref, VALUE val)
{
    int nth;
    VALUE match;
    long start, end, len;
    rb_encoding *enc;
    struct re_registers *regs;

    if (rb_reg_search(re, str, 0, 0) < 0) {
        rb_raise(rb_eIndexError, "regexp not matched");
    }
    match = rb_backref_get();
    nth = rb_reg_backref_number(match, backref);
    regs = RMATCH_REGS(match);
    if (nth >= regs->num_regs) {
      out_of_range:
        rb_raise(rb_eIndexError, "index %d out of regexp", nth);
    }
    if (nth < 0) {
        if (-nth >= regs->num_regs) {
            goto out_of_range;
        }
        nth += regs->num_regs;
    }

    start = BEG(nth);
    if (start == -1) {
        rb_raise(rb_eIndexError, "regexp group %d not matched", nth);
    }
    end = END(nth);
    len = end - start;
    StringValue(val);
    enc = rb_enc_check(str, val);
    rb_str_splice_0(str, start, len, val);
    rb_enc_associate(str, enc);
}

static VALUE
rb_str_aset(VALUE str, VALUE indx, VALUE val)
{
    long idx, beg;

    if (FIXNUM_P(indx)) {
        idx = FIX2LONG(indx);
      num_index:
        rb_str_splice(str, idx, 1, val);
        return val;
    }

    if (SPECIAL_CONST_P(indx)) goto generic;
    switch (TYPE(indx)) {
      case T_REGEXP:
        rb_str_subpat_set(str, indx, INT2FIX(0), val);
        return val;

      case T_STRING:
        beg = rb_str_index(str, indx, 0);
        if (beg < 0) {
            rb_raise(rb_eIndexError, "string not matched");
        }
        beg = rb_str_sublen(str, beg);
        rb_str_splice(str, beg, str_strlen(indx, 0), val);
        return val;

      generic:
      default:
        /* check if indx is Range */
        {
            long beg, len;
            if (rb_range_beg_len(indx, &beg, &len, str_strlen(str, 0), 2)) {
                rb_str_splice(str, beg, len, val);
                return val;
            }
        }
        idx = NUM2LONG(indx);
        goto num_index;
    }
}

/*
 *  call-seq:
 *     str[fixnum] = new_str
 *     str[fixnum, fixnum] = new_str
 *     str[range] = aString
 *     str[regexp] = new_str
 *     str[regexp, fixnum] = new_str
 *     str[regexp, name] = new_str
 *     str[other_str] = new_str
 *
 *  Element Assignment---Replaces some or all of the content of <i>str</i>. The
 *  portion of the string affected is determined using the same criteria as
 *  <code>String#[]</code>. If the replacement string is not the same length as
 *  the text it is replacing, the string will be adjusted accordingly. If the
 *  regular expression or string is used as the index doesn't match a position
 *  in the string, <code>IndexError</code> is raised. If the regular expression
 *  form is used, the optional second <code>Fixnum</code> allows you to specify
 *  which portion of the match to replace (effectively using the
 *  <code>MatchData</code> indexing rules. The forms that take a
 *  <code>Fixnum</code> will raise an <code>IndexError</code> if the value is
 *  out of range; the <code>Range</code> form will raise a
 *  <code>RangeError</code>, and the <code>Regexp</code> and <code>String</code>
 *  will raise an <code>IndexError</code> on negative match.
 */

static VALUE
rb_str_aset_m(int argc, VALUE *argv, VALUE str)
{
    if (argc == 3) {
        if (RB_TYPE_P(argv[0], T_REGEXP)) {
            rb_str_subpat_set(str, argv[0], argv[1], argv[2]);
        }
        else {
            rb_str_splice(str, NUM2LONG(argv[0]), NUM2LONG(argv[1]), argv[2]);
        }
        return argv[2];
    }
    rb_check_arity(argc, 2, 3);
    return rb_str_aset(str, argv[0], argv[1]);
}

/*
 *  call-seq:
 *     str.insert(index, other_str)   -> str
 *
 *  Inserts <i>other_str</i> before the character at the given
 *  <i>index</i>, modifying <i>str</i>. Negative indices count from the
 *  end of the string, and insert <em>after</em> the given character.
 *  The intent is insert <i>aString</i> so that it starts at the given
 *  <i>index</i>.
 *
 *     "abcd".insert(0, 'X')    #=> "Xabcd"
 *     "abcd".insert(3, 'X')    #=> "abcXd"
 *     "abcd".insert(4, 'X')    #=> "abcdX"
 *     "abcd".insert(-3, 'X')   #=> "abXcd"
 *     "abcd".insert(-1, 'X')   #=> "abcdX"
 */

static VALUE
rb_str_insert(VALUE str, VALUE idx, VALUE str2)
{
    long pos = NUM2LONG(idx);

    if (pos == -1) {
        return rb_str_append(str, str2);
    }
    else if (pos < 0) {
        pos++;
    }
    rb_str_splice(str, pos, 0, str2);
    return str;
}


/*
 *  call-seq:
 *     str.slice!(fixnum)           -> fixnum or nil
 *     str.slice!(fixnum, fixnum)   -> new_str or nil
 *     str.slice!(range)            -> new_str or nil
 *     str.slice!(regexp)           -> new_str or nil
 *     str.slice!(other_str)        -> new_str or nil
 *
 *  Deletes the specified portion from <i>str</i>, and returns the portion
 *  deleted.
 *
 *     string = "this is a string"
 *     string.slice!(2)        #=> "i"
 *     string.slice!(3..6)     #=> " is "
 *     string.slice!(/s.*t/)   #=> "sa st"
 *     string.slice!("r")      #=> "r"
 *     string                  #=> "thing"
 */

static VALUE
rb_str_slice_bang(int argc, VALUE *argv, VALUE str)
{
    VALUE result;
    VALUE buf[3];
    int i;

    rb_check_arity(argc, 1, 2);
    for (i=0; i<argc; i++) {
        buf[i] = argv[i];
    }
    str_modify_keep_cr(str);
    result = rb_str_aref_m(argc, buf, str);
    if (!NIL_P(result)) {
        buf[i] = rb_str_new(0,0);
        rb_str_aset_m(argc+1, buf, str);
    }
    return result;
}

static VALUE
get_pat(VALUE pat, int quote)
{
    VALUE val;

    switch (TYPE(pat)) {
      case T_REGEXP:
        return pat;

      case T_STRING:
        break;

      default:
        val = rb_check_string_type(pat);
        if (NIL_P(val)) {
            Check_Type(pat, T_REGEXP);
        }
        pat = val;
    }

    if (quote) {
        pat = rb_reg_quote(pat);
    }

    return rb_reg_regcomp(pat);
}


/*
 *  call-seq:
 *     str.sub!(pattern, replacement)          -> str or nil
 *     str.sub!(pattern) {|match| block }      -> str or nil
 *
 *  Performs the same substitution as String#sub in-place.
 *
 *  Returns +str+ if a substitution was performed or +nil+ if no substitution
 *  was performed.
 */

static VALUE
rb_str_sub_bang(int argc, VALUE *argv, VALUE str)
{
    VALUE pat, repl, hash = Qnil;
    int iter = 0;
    int tainted = 0;
    long plen;
    int min_arity = rb_block_given_p() ? 1 : 2;

    rb_check_arity(argc, min_arity, 2);
    if (argc == 1) {
        iter = 1;
    }
    else {
        repl = argv[1];
        hash = rb_check_hash_type(argv[1]);
        if (NIL_P(hash)) {
            StringValue(repl);
        }
        tainted = OBJ_TAINTED_RAW(repl);
    }

    pat = get_pat(argv[0], 1);
    str_modifiable(str);
    if (rb_reg_search(pat, str, 0, 0) >= 0) {
        rb_encoding *enc;
        int cr = ENC_CODERANGE(str);
        VALUE match = rb_backref_get();
        struct re_registers *regs = RMATCH_REGS(match);
        long beg0 = BEG(0);
        long end0 = END(0);
        char *p, *rp;
        long len, rlen;

        if (iter || !NIL_P(hash)) {
            p = RSTRING_PTR(str); len = RSTRING_LEN(str);

            if (iter) {
                repl = rb_obj_as_string(rb_yield(rb_reg_nth_match(0, match)));
            }
            else {
                repl = rb_hash_aref(hash, rb_str_subseq(str, beg0, end0 - beg0));
                repl = rb_obj_as_string(repl);
            }
            str_mod_check(str, p, len);
            rb_check_frozen(str);
        }
        else {
            repl = rb_reg_regsub(repl, str, regs, pat);
        }
        enc = rb_enc_compatible(str, repl);
        if (!enc) {
            rb_encoding *str_enc = STR_ENC_GET(str);
            p = RSTRING_PTR(str); len = RSTRING_LEN(str);
            if (coderange_scan(p, beg0, str_enc) != ENC_CODERANGE_7BIT ||
                coderange_scan(p+end0, len-end0, str_enc) != ENC_CODERANGE_7BIT) {
                rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
                         rb_enc_name(str_enc),
                         rb_enc_name(STR_ENC_GET(repl)));
            }
            enc = STR_ENC_GET(repl);
        }
        rb_str_modify(str);
        rb_enc_associate(str, enc);
        tainted |= OBJ_TAINTED_RAW(repl);
        if (ENC_CODERANGE_UNKNOWN < cr && cr < ENC_CODERANGE_BROKEN) {
            int cr2 = ENC_CODERANGE(repl);
            if (cr2 == ENC_CODERANGE_BROKEN ||
                (cr == ENC_CODERANGE_VALID && cr2 == ENC_CODERANGE_7BIT))
                cr = ENC_CODERANGE_UNKNOWN;
            else
                cr = cr2;
        }
        plen = end0 - beg0;
        rp = RSTRING_PTR(repl); rlen = RSTRING_LEN(repl);
        len = RSTRING_LEN(str);
        if (rlen > plen) {
            RESIZE_CAPA(str, len + rlen - plen);
        }
        p = RSTRING_PTR(str);
        if (rlen != plen) {
            memmove(p + beg0 + rlen, p + beg0 + plen, len - beg0 - plen);
        }
        memcpy(p + beg0, rp, rlen);
        len += rlen - plen;
        STR_SET_LEN(str, len);
        RSTRING_PTR(str)[len] = '\0';
        ENC_CODERANGE_SET(str, cr);
        FL_SET_RAW(str, tainted);

        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.sub(pattern, replacement)         -> new_str
 *     str.sub(pattern, hash)                -> new_str
 *     str.sub(pattern) {|match| block }     -> new_str
 *
 *  Returns a copy of +str+ with the _first_ occurrence of +pattern+
 *  replaced by the second argument. The +pattern+ is typically a Regexp; if
 *  given as a String, any regular expression metacharacters it contains will
 *  be interpreted literally, e.g. <code>'\\\d'</code> will match a backlash
 *  followed by 'd', instead of a digit.
 *
 *  If +replacement+ is a String it will be substituted for the matched text.
 *  It may contain back-references to the pattern's capture groups of the form
 *  <code>"\\d"</code>, where <i>d</i> is a group number, or
 *  <code>"\\k<n>"</code>, where <i>n</i> is a group name. If it is a
 *  double-quoted string, both back-references must be preceded by an
 *  additional backslash. However, within +replacement+ the special match
 *  variables, such as <code>&$</code>, will not refer to the current match.
 *  If +replacement+ is a String that looks like a pattern's capture group but
 *  is actaully not a pattern capture group e.g. <code>"\\'"</code>, then it
 *  will have to be preceded by two backslashes like so <code>"\\\\'"</code>.
 *
 *  If the second argument is a Hash, and the matched text is one of its keys,
 *  the corresponding value is the replacement string.
 *
 *  In the block form, the current match string is passed in as a parameter,
 *  and variables such as <code>$1</code>, <code>$2</code>, <code>$`</code>,
 *  <code>$&</code>, and <code>$'</code> will be set appropriately. The value
 *  returned by the block will be substituted for the match on each call.
 *
 *  The result inherits any tainting in the original string or any supplied
 *  replacement string.
 *
 *     "hello".sub(/[aeiou]/, '*')                  #=> "h*llo"
 *     "hello".sub(/([aeiou])/, '<\1>')             #=> "h<e>llo"
 *     "hello".sub(/./) {|s| s.ord.to_s + ' ' }     #=> "104 ello"
 *     "hello".sub(/(?<foo>[aeiou])/, '*\k<foo>*')  #=> "h*e*llo"
 *     'Is SHELL your preferred shell?'.sub(/[[:upper:]]{2,}/, ENV)
 *      #=> "Is /bin/bash your preferred shell?"
 */

static VALUE
rb_str_sub(int argc, VALUE *argv, VALUE str)
{
    str = rb_str_dup(str);
    rb_str_sub_bang(argc, argv, str);
    return str;
}

static VALUE
str_gsub(int argc, VALUE *argv, VALUE str, int bang)
{
    VALUE pat, val, repl, match, dest, hash = Qnil;
    struct re_registers *regs;
    long beg, n;
    long beg0, end0;
    long offset, blen, slen, len, last;
    int iter = 0;
    char *sp, *cp;
    int tainted = 0;
    rb_encoding *str_enc;

    switch (argc) {
      case 1:
        RETURN_ENUMERATOR(str, argc, argv);
        iter = 1;
        break;
      case 2:
        repl = argv[1];
        hash = rb_check_hash_type(argv[1]);
        if (NIL_P(hash)) {
            StringValue(repl);
        }
        tainted = OBJ_TAINTED_RAW(repl);
        break;
      default:
        rb_check_arity(argc, 1, 2);
    }

    pat = get_pat(argv[0], 1);
    beg = rb_reg_search(pat, str, 0, 0);
    if (beg < 0) {
        if (bang) return Qnil;  /* no match, no substitution */
        return rb_str_dup(str);
    }

    offset = 0;
    n = 0;
    blen = RSTRING_LEN(str) + 30; /* len + margin */
    dest = rb_str_buf_new(blen);
    sp = RSTRING_PTR(str);
    slen = RSTRING_LEN(str);
    cp = sp;
    str_enc = STR_ENC_GET(str);
    rb_enc_associate(dest, str_enc);
    ENC_CODERANGE_SET(dest, rb_enc_asciicompat(str_enc) ? ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID);

    do {
        n++;
        match = rb_backref_get();
        regs = RMATCH_REGS(match);
        beg0 = BEG(0);
        end0 = END(0);
        if (iter || !NIL_P(hash)) {
            if (iter) {
                val = rb_obj_as_string(rb_yield(rb_reg_nth_match(0, match)));
            }
            else {
                val = rb_hash_aref(hash, rb_str_subseq(str, BEG(0), END(0) - BEG(0)));
                val = rb_obj_as_string(val);
            }
            str_mod_check(str, sp, slen);
            if (val == dest) {  /* paranoid check [ruby-dev:24827] */
                rb_raise(rb_eRuntimeError, "block should not cheat");
            }
        }
        else {
            val = rb_reg_regsub(repl, str, regs, pat);
        }

        tainted |= OBJ_TAINTED_RAW(val);

        len = beg0 - offset;    /* copy pre-match substr */
        if (len) {
            rb_enc_str_buf_cat(dest, cp, len, str_enc);
        }

        rb_str_buf_append(dest, val);

        last = offset;
        offset = end0;
        if (beg0 == end0) {
            /*
             * Always consume at least one character of the input string
             * in order to prevent infinite loops.
             */
            if (RSTRING_LEN(str) <= end0) break;
            len = rb_enc_fast_mbclen(RSTRING_PTR(str)+end0, RSTRING_END(str), str_enc);
            rb_enc_str_buf_cat(dest, RSTRING_PTR(str)+end0, len, str_enc);
            offset = end0 + len;
        }
        cp = RSTRING_PTR(str) + offset;
        if (offset > RSTRING_LEN(str)) break;
        beg = rb_reg_search(pat, str, offset, 0);
    } while (beg >= 0);
    if (RSTRING_LEN(str) > offset) {
        rb_enc_str_buf_cat(dest, cp, RSTRING_LEN(str) - offset, str_enc);
    }
    rb_reg_search(pat, str, last, 0);
    if (bang) {
        rb_str_shared_replace(str, dest);
    }
    else {
        RBASIC_SET_CLASS(dest, rb_obj_class(str));
        tainted |= OBJ_TAINTED_RAW(str);
        str = dest;
    }

    FL_SET_RAW(str, tainted);
    return str;
}


/*
 *  call-seq:
 *     str.gsub!(pattern, replacement)        -> str or nil
 *     str.gsub!(pattern) {|match| block }    -> str or nil
 *     str.gsub!(pattern)                     -> an_enumerator
 *
 *  Performs the substitutions of <code>String#gsub</code> in place, returning
 *  <i>str</i>, or <code>nil</code> if no substitutions were performed.
 *  If no block and no <i>replacement</i> is given, an enumerator is returned instead.
 */

static VALUE
rb_str_gsub_bang(int argc, VALUE *argv, VALUE str)
{
    str_modify_keep_cr(str);
    return str_gsub(argc, argv, str, 1);
}


/*
 *  call-seq:
 *     str.gsub(pattern, replacement)       -> new_str
 *     str.gsub(pattern, hash)              -> new_str
 *     str.gsub(pattern) {|match| block }   -> new_str
 *     str.gsub(pattern)                    -> enumerator
 *
 *  Returns a copy of <i>str</i> with the <em>all</em> occurrences of
 *  <i>pattern</i> substituted for the second argument. The <i>pattern</i> is
 *  typically a <code>Regexp</code>; if given as a <code>String</code>, any
 *  regular expression metacharacters it contains will be interpreted
 *  literally, e.g. <code>'\\\d'</code> will match a backlash followed by 'd',
 *  instead of a digit.
 *
 *  If <i>replacement</i> is a <code>String</code> it will be substituted for
 *  the matched text. It may contain back-references to the pattern's capture
 *  groups of the form <code>\\\d</code>, where <i>d</i> is a group number, or
 *  <code>\\\k<n></code>, where <i>n</i> is a group name. If it is a
 *  double-quoted string, both back-references must be preceded by an
 *  additional backslash. However, within <i>replacement</i> the special match
 *  variables, such as <code>$&</code>, will not refer to the current match.
 *
 *  If the second argument is a <code>Hash</code>, and the matched text is one
 *  of its keys, the corresponding value is the replacement string.
 *
 *  In the block form, the current match string is passed in as a parameter,
 *  and variables such as <code>$1</code>, <code>$2</code>, <code>$`</code>,
 *  <code>$&</code>, and <code>$'</code> will be set appropriately. The value
 *  returned by the block will be substituted for the match on each call.
 *
 *  The result inherits any tainting in the original string or any supplied
 *  replacement string.
 *
 *  When neither a block nor a second argument is supplied, an
 *  <code>Enumerator</code> is returned.
 *
 *     "hello".gsub(/[aeiou]/, '*')                  #=> "h*ll*"
 *     "hello".gsub(/([aeiou])/, '<\1>')             #=> "h<e>ll<o>"
 *     "hello".gsub(/./) {|s| s.ord.to_s + ' '}      #=> "104 101 108 108 111 "
 *     "hello".gsub(/(?<foo>[aeiou])/, '{\k<foo>}')  #=> "h{e}ll{o}"
 *     'hello'.gsub(/[eo]/, 'e' => 3, 'o' => '*')    #=> "h3ll*"
 */

static VALUE
rb_str_gsub(int argc, VALUE *argv, VALUE str)
{
    return str_gsub(argc, argv, str, 0);
}


/*
 *  call-seq:
 *     str.replace(other_str)   -> str
 *
 *  Replaces the contents and taintedness of <i>str</i> with the corresponding
 *  values in <i>other_str</i>.
 *
 *     s = "hello"         #=> "hello"
 *     s.replace "world"   #=> "world"
 */

VALUE
rb_str_replace(VALUE str, VALUE str2)
{
    str_modifiable(str);
    if (str == str2) return str;

    StringValue(str2);
    str_discard(str);
    return str_replace(str, str2);
}

/*
 *  call-seq:
 *     string.clear    ->  string
 *
 *  Makes string empty.
 *
 *     a = "abcde"
 *     a.clear    #=> ""
 */

static VALUE
rb_str_clear(VALUE str)
{
    str_discard(str);
    STR_SET_EMBED(str);
    STR_SET_EMBED_LEN(str, 0);
    RSTRING_PTR(str)[0] = 0;
    if (rb_enc_asciicompat(STR_ENC_GET(str)))
        ENC_CODERANGE_SET(str, ENC_CODERANGE_7BIT);
    else
        ENC_CODERANGE_SET(str, ENC_CODERANGE_VALID);
    return str;
}

/*
 *  call-seq:
 *     string.chr    ->  string
 *
 *  Returns a one-character string at the beginning of the string.
 *
 *     a = "abcde"
 *     a.chr    #=> "a"
 */

static VALUE
rb_str_chr(VALUE str)
{
    return rb_str_substr(str, 0, 1);
}

/*
 *  call-seq:
 *     str.getbyte(index)          -> 0 .. 255
 *
 *  returns the <i>index</i>th byte as an integer.
 */
static VALUE
rb_str_getbyte(VALUE str, VALUE index)
{
    long pos = NUM2LONG(index);

    if (pos < 0)
        pos += RSTRING_LEN(str);
    if (pos < 0 ||  RSTRING_LEN(str) <= pos)
        return Qnil;

    return INT2FIX((unsigned char)RSTRING_PTR(str)[pos]);
}

/*
 *  call-seq:
 *     str.setbyte(index, integer) -> integer
 *
 *  modifies the <i>index</i>th byte as <i>integer</i>.
 */
static VALUE
rb_str_setbyte(VALUE str, VALUE index, VALUE value)
{
    long pos = NUM2LONG(index);
    int byte = NUM2INT(value);

    rb_str_modify(str);

    if (pos < -RSTRING_LEN(str) || RSTRING_LEN(str) <= pos)
        rb_raise(rb_eIndexError, "index %ld out of string", pos);
    if (pos < 0)
        pos += RSTRING_LEN(str);

    RSTRING_PTR(str)[pos] = byte;

    return value;
}

static VALUE
str_byte_substr(VALUE str, long beg, long len)
{
    char *p, *s = RSTRING_PTR(str);
    long n = RSTRING_LEN(str);
    VALUE str2;

    if (beg > n || len < 0) return Qnil;
    if (beg < 0) {
        beg += n;
        if (beg < 0) return Qnil;
    }
    if (beg + len > n)
        len = n - beg;
    if (len <= 0) {
        len = 0;
        p = 0;
    }
    else
        p = s + beg;

    if (len > RSTRING_EMBED_LEN_MAX && beg + len == n) {
        str2 = rb_str_new4(str);
        str2 = str_new3(rb_obj_class(str2), str2);
        RSTRING(str2)->as.heap.ptr += RSTRING(str2)->as.heap.len - len;
        RSTRING(str2)->as.heap.len = len;
    }
    else {
        str2 = rb_str_new5(str, p, len);
    }

    str_enc_copy(str2, str);

    if (RSTRING_LEN(str2) == 0) {
        if (!rb_enc_asciicompat(STR_ENC_GET(str)))
            ENC_CODERANGE_SET(str2, ENC_CODERANGE_VALID);
        else
            ENC_CODERANGE_SET(str2, ENC_CODERANGE_7BIT);
    }
    else {
        switch (ENC_CODERANGE(str)) {
          case ENC_CODERANGE_7BIT:
            ENC_CODERANGE_SET(str2, ENC_CODERANGE_7BIT);
            break;
          default:
            ENC_CODERANGE_SET(str2, ENC_CODERANGE_UNKNOWN);
            break;
        }
    }

    OBJ_INFECT_RAW(str2, str);

    return str2;
}

static VALUE
str_byte_aref(VALUE str, VALUE indx)
{
    long idx;
    switch (TYPE(indx)) {
      case T_FIXNUM:
        idx = FIX2LONG(indx);

      num_index:
        str = str_byte_substr(str, idx, 1);
        if (NIL_P(str) || RSTRING_LEN(str) == 0) return Qnil;
        return str;

      default:
        /* check if indx is Range */
        {
            long beg, len = RSTRING_LEN(str);

            switch (rb_range_beg_len(indx, &beg, &len, len, 0)) {
              case Qfalse:
                break;
              case Qnil:
                return Qnil;
              default:
                return str_byte_substr(str, beg, len);
            }
        }
        idx = NUM2LONG(indx);
        goto num_index;
    }

    UNREACHABLE;
}

/*
 *  call-seq:
 *     str.byteslice(fixnum)           -> new_str or nil
 *     str.byteslice(fixnum, fixnum)   -> new_str or nil
 *     str.byteslice(range)            -> new_str or nil
 *
 *  Byte Reference---If passed a single <code>Fixnum</code>, returns a
 *  substring of one byte at that position. If passed two <code>Fixnum</code>
 *  objects, returns a substring starting at the offset given by the first, and
 *  a length given by the second. If given a <code>Range</code>, a substring containing
 *  bytes at offsets given by the range is returned. In all three cases, if
 *  an offset is negative, it is counted from the end of <i>str</i>. Returns
 *  <code>nil</code> if the initial offset falls outside the string, the length
 *  is negative, or the beginning of the range is greater than the end.
 *  The encoding of the resulted string keeps original encoding.
 *
 *     "hello".byteslice(1)     #=> "e"
 *     "hello".byteslice(-1)    #=> "o"
 *     "hello".byteslice(1, 2)  #=> "el"
 *     "\x80\u3042".byteslice(1, 3) #=> "\u3042"
 *     "\x03\u3042\xff".byteslice(1..3) #=> "\u3042"
 */

static VALUE
rb_str_byteslice(int argc, VALUE *argv, VALUE str)
{
    if (argc == 2) {
        return str_byte_substr(str, NUM2LONG(argv[0]), NUM2LONG(argv[1]));
    }
    rb_check_arity(argc, 1, 2);
    return str_byte_aref(str, argv[0]);
}

/*
 *  call-seq:
 *     str.reverse   -> new_str
 *
 *  Returns a new string with the characters from <i>str</i> in reverse order.
 *
 *     "stressed".reverse   #=> "desserts"
 */

static VALUE
rb_str_reverse(VALUE str)
{
    rb_encoding *enc;
    VALUE rev;
    char *s, *e, *p;
    int cr;

    if (RSTRING_LEN(str) <= 1) return rb_str_dup(str);
    enc = STR_ENC_GET(str);
    rev = rb_str_new5(str, 0, RSTRING_LEN(str));
    s = RSTRING_PTR(str); e = RSTRING_END(str);
    p = RSTRING_END(rev);
    cr = ENC_CODERANGE(str);

    if (RSTRING_LEN(str) > 1) {
        if (single_byte_optimizable(str)) {
            while (s < e) {
                *--p = *s++;
            }
        }
        else if (cr == ENC_CODERANGE_VALID) {
            while (s < e) {
                int clen = rb_enc_fast_mbclen(s, e, enc);

                p -= clen;
                memcpy(p, s, clen);
                s += clen;
            }
        }
        else {
            cr = rb_enc_asciicompat(enc) ?
                ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID;
            while (s < e) {
                int clen = rb_enc_mbclen(s, e, enc);

                if (clen > 1 || (*s & 0x80)) cr = ENC_CODERANGE_UNKNOWN;
                p -= clen;
                memcpy(p, s, clen);
                s += clen;
            }
        }
    }
    STR_SET_LEN(rev, RSTRING_LEN(str));
    OBJ_INFECT_RAW(rev, str);
    str_enc_copy(rev, str);
    ENC_CODERANGE_SET(rev, cr);

    return rev;
}


/*
 *  call-seq:
 *     str.reverse!   -> str
 *
 *  Reverses <i>str</i> in place.
 */

static VALUE
rb_str_reverse_bang(VALUE str)
{
    if (RSTRING_LEN(str) > 1) {
        if (single_byte_optimizable(str)) {
            char *s, *e, c;

            str_modify_keep_cr(str);
            s = RSTRING_PTR(str);
            e = RSTRING_END(str) - 1;
            while (s < e) {
                c = *s;
                *s++ = *e;
                *e-- = c;
            }
        }
        else {
            rb_str_shared_replace(str, rb_str_reverse(str));
        }
    }
    else {
        str_modify_keep_cr(str);
    }
    return str;
}


/*
 *  call-seq:
 *     str.include? other_str   -> true or false
 *
 *  Returns <code>true</code> if <i>str</i> contains the given string or
 *  character.
 *
 *     "hello".include? "lo"   #=> true
 *     "hello".include? "ol"   #=> false
 *     "hello".include? ?h     #=> true
 */

static VALUE
rb_str_include(VALUE str, VALUE arg)
{
    long i;

    StringValue(arg);
    i = rb_str_index(str, arg, 0);

    if (i == -1) return Qfalse;
    return Qtrue;
}


/*
 *  call-seq:
 *     str.to_i(base=10)   -> integer
 *
 *  Returns the result of interpreting leading characters in <i>str</i> as an
 *  integer base <i>base</i> (between 2 and 36). Extraneous characters past the
 *  end of a valid number are ignored. If there is not a valid number at the
 *  start of <i>str</i>, <code>0</code> is returned. This method never raises an
 *  exception when <i>base</i> is valid.
 *
 *     "12345".to_i             #=> 12345
 *     "99 red balloons".to_i   #=> 99
 *     "0a".to_i                #=> 0
 *     "0a".to_i(16)            #=> 10
 *     "hello".to_i             #=> 0
 *     "1100101".to_i(2)        #=> 101
 *     "1100101".to_i(8)        #=> 294977
 *     "1100101".to_i(10)       #=> 1100101
 *     "1100101".to_i(16)       #=> 17826049
 */

static VALUE
rb_str_to_i(int argc, VALUE *argv, VALUE str)
{
    int base;

    if (argc == 0) base = 10;
    else {
        VALUE b;

        rb_scan_args(argc, argv, "01", &b);
        base = NUM2INT(b);
    }
    if (base < 0) {
        rb_raise(rb_eArgError, "invalid radix %d", base);
    }
    return rb_str_to_inum(str, base, FALSE);
}


/*
 *  call-seq:
 *     str.to_f   -> float
 *
 *  Returns the result of interpreting leading characters in <i>str</i> as a
 *  floating point number. Extraneous characters past the end of a valid number
 *  are ignored. If there is not a valid number at the start of <i>str</i>,
 *  <code>0.0</code> is returned. This method never raises an exception.
 *
 *     "123.45e1".to_f        #=> 1234.5
 *     "45.67 degrees".to_f   #=> 45.67
 *     "thx1138".to_f         #=> 0.0
 */

static VALUE
rb_str_to_f(VALUE str)
{
    return DBL2NUM(rb_str_to_dbl(str, FALSE));
}


/*
 *  call-seq:
 *     str.to_s     -> str
 *     str.to_str   -> str
 *
 *  Returns the receiver.
 */

static VALUE
rb_str_to_s(VALUE str)
{
    if (rb_obj_class(str) != rb_cString) {
        return str_duplicate(rb_cString, str);
    }
    return str;
}

#if 0
static void
str_cat_char(VALUE str, unsigned int c, rb_encoding *enc)
{
    char s[RUBY_MAX_CHAR_LEN];
    int n = rb_enc_codelen(c, enc);

    rb_enc_mbcput(c, s, enc);
    rb_enc_str_buf_cat(str, s, n, enc);
}
#endif

#define CHAR_ESC_LEN 13 /* sizeof(\x{ hex of 32bit unsigned int } \0) */

int
rb_str_buf_cat_escaped_char(VALUE result, unsigned int c, int unicode_p)
{
    char buf[CHAR_ESC_LEN + 1];
    int l;

#if SIZEOF_INT > 4
    c &= 0xffffffff;
#endif
    if (unicode_p) {
        if (c < 0x7F && ISPRINT(c)) {
            snprintf(buf, CHAR_ESC_LEN, "%c", c);
        }
        else if (c < 0x10000) {
            snprintf(buf, CHAR_ESC_LEN, "\\u%04X", c);
        }
        else {
            snprintf(buf, CHAR_ESC_LEN, "\\u{%X}", c);
        }
    }
    else {
        if (c < 0x100) {
            snprintf(buf, CHAR_ESC_LEN, "\\x%02X", c);
        }
        else {
            snprintf(buf, CHAR_ESC_LEN, "\\x{%X}", c);
        }
    }
    l = (int)strlen(buf);       /* CHAR_ESC_LEN cannot exceed INT_MAX */
    rb_str_buf_cat(result, buf, l);
    return l;
}

/*
 * call-seq:
 *   str.inspect   -> string
 *
 * Returns a printable version of _str_, surrounded by quote marks,
 * with special characters escaped.
 *
 *    str = "hello"
 *    str[3] = "\b"
 *    str.inspect       #=> "\"hel\\bo\""
 */

VALUE
rb_str_inspect(VALUE str)
{
    int encidx = ENCODING_GET(str);
    rb_encoding *enc = rb_enc_from_index(encidx), *actenc;
    const char *p, *pend, *prev;
    char buf[CHAR_ESC_LEN + 1];
    VALUE result = rb_str_buf_new(0);
    rb_encoding *resenc = rb_default_internal_encoding();
    int unicode_p = rb_enc_unicode_p(enc);
    int asciicompat = rb_enc_asciicompat(enc);

    if (resenc == NULL) resenc = rb_default_external_encoding();
    if (!rb_enc_asciicompat(resenc)) resenc = rb_usascii_encoding();
    rb_enc_associate(result, resenc);
    str_buf_cat2(result, "\"");

    p = RSTRING_PTR(str); pend = RSTRING_END(str);
    prev = p;
    actenc = get_actual_encoding(encidx, str);
    if (actenc != enc) {
        enc = actenc;
        if (unicode_p) unicode_p = rb_enc_unicode_p(enc);
    }
    while (p < pend) {
        unsigned int c, cc;
        int n;

        n = rb_enc_precise_mbclen(p, pend, enc);
        if (!MBCLEN_CHARFOUND_P(n)) {
            if (p > prev) str_buf_cat(result, prev, p - prev);
            n = rb_enc_mbminlen(enc);
            if (pend < p + n)
                n = (int)(pend - p);
            while (n--) {
                snprintf(buf, CHAR_ESC_LEN, "\\x%02X", *p & 0377);
                str_buf_cat(result, buf, strlen(buf));
                prev = ++p;
            }
            continue;
        }
        n = MBCLEN_CHARFOUND_LEN(n);
        c = rb_enc_mbc_to_codepoint(p, pend, enc);
        p += n;
        if ((asciicompat || unicode_p) &&
          (c == '"'|| c == '\\' ||
            (c == '#' &&
             p < pend &&
             MBCLEN_CHARFOUND_P(rb_enc_precise_mbclen(p,pend,enc)) &&
             (cc = rb_enc_codepoint(p,pend,enc),
              (cc == '$' || cc == '@' || cc == '{'))))) {
            if (p - n > prev) str_buf_cat(result, prev, p - n - prev);
            str_buf_cat2(result, "\\");
            if (asciicompat || enc == resenc) {
                prev = p - n;
                continue;
            }
        }
        switch (c) {
          case '\n': cc = 'n'; break;
          case '\r': cc = 'r'; break;
          case '\t': cc = 't'; break;
          case '\f': cc = 'f'; break;
          case '\013': cc = 'v'; break;
          case '\010': cc = 'b'; break;
          case '\007': cc = 'a'; break;
          case 033: cc = 'e'; break;
          default: cc = 0; break;
        }
        if (cc) {
            if (p - n > prev) str_buf_cat(result, prev, p - n - prev);
            buf[0] = '\\';
            buf[1] = (char)cc;
            str_buf_cat(result, buf, 2);
            prev = p;
            continue;
        }
        if ((enc == resenc && rb_enc_isprint(c, enc)) ||
            (asciicompat && rb_enc_isascii(c, enc) && ISPRINT(c))) {
            continue;
        }
        else {
            if (p - n > prev) str_buf_cat(result, prev, p - n - prev);
            rb_str_buf_cat_escaped_char(result, c, unicode_p);
            prev = p;
            continue;
        }
    }
    if (p > prev) str_buf_cat(result, prev, p - prev);
    str_buf_cat2(result, "\"");

    OBJ_INFECT_RAW(result, str);
    return result;
}

#define IS_EVSTR(p,e) ((p) < (e) && (*(p) == '$' || *(p) == '@' || *(p) == '{'))

/*
 *  call-seq:
 *     str.dump   -> new_str
 *
 *  Produces a version of +str+ with all non-printing characters replaced by
 *  <code>\nnn</code> notation and all special characters escaped.
 *
 *    "hello \n ''".dump  #=> "\"hello \\n ''\"
 */

VALUE
rb_str_dump(VALUE str)
{
    rb_encoding *enc = rb_enc_get(str);
    long len;
    const char *p, *pend;
    char *q, *qend;
    VALUE result;
    int u8 = (enc == rb_utf8_encoding());

    len = 2;                    /* "" */
    p = RSTRING_PTR(str); pend = p + RSTRING_LEN(str);
    while (p < pend) {
        unsigned char c = *p++;
        switch (c) {
          case '"':  case '\\':
          case '\n': case '\r':
          case '\t': case '\f':
          case '\013': case '\010': case '\007': case '\033':
            len += 2;
            break;

          case '#':
            len += IS_EVSTR(p, pend) ? 2 : 1;
            break;

          default:
            if (ISPRINT(c)) {
                len++;
            }
            else {
                if (u8 && c > 0x7F) {   /* \u{NN} */
                    int n = rb_enc_precise_mbclen(p-1, pend, enc);
                    if (MBCLEN_CHARFOUND_P(n)) {
                        unsigned int cc = rb_enc_mbc_to_codepoint(p-1, pend, enc);
                        while (cc >>= 4) len++;
                        len += 5;
                        p += MBCLEN_CHARFOUND_LEN(n)-1;
                        break;
                    }
                }
                len += 4;       /* \xNN */
            }
            break;
        }
    }
    if (!rb_enc_asciicompat(enc)) {
        len += 19;              /* ".force_encoding('')" */
        len += strlen(enc->name);
    }

    result = rb_str_new5(str, 0, len);
    p = RSTRING_PTR(str); pend = p + RSTRING_LEN(str);
    q = RSTRING_PTR(result); qend = q + len + 1;

    *q++ = '"';
    while (p < pend) {
        unsigned char c = *p++;

        if (c == '"' || c == '\\') {
            *q++ = '\\';
            *q++ = c;
        }
        else if (c == '#') {
            if (IS_EVSTR(p, pend)) *q++ = '\\';
            *q++ = '#';
        }
        else if (c == '\n') {
            *q++ = '\\';
            *q++ = 'n';
        }
        else if (c == '\r') {
            *q++ = '\\';
            *q++ = 'r';
        }
        else if (c == '\t') {
            *q++ = '\\';
            *q++ = 't';
        }
        else if (c == '\f') {
            *q++ = '\\';
            *q++ = 'f';
        }
        else if (c == '\013') {
            *q++ = '\\';
            *q++ = 'v';
        }
        else if (c == '\010') {
            *q++ = '\\';
            *q++ = 'b';
        }
        else if (c == '\007') {
            *q++ = '\\';
            *q++ = 'a';
        }
        else if (c == '\033') {
            *q++ = '\\';
            *q++ = 'e';
        }
        else if (ISPRINT(c)) {
            *q++ = c;
        }
        else {
            *q++ = '\\';
            if (u8) {
                int n = rb_enc_precise_mbclen(p-1, pend, enc) - 1;
                if (MBCLEN_CHARFOUND_P(n)) {
                    int cc = rb_enc_mbc_to_codepoint(p-1, pend, enc);
                    p += n;
                    snprintf(q, qend-q, "u{%x}", cc);
                    q += strlen(q);
                    continue;
                }
            }
            snprintf(q, qend-q, "x%02X", c);
            q += 3;
        }
    }
    *q++ = '"';
    *q = '\0';
    if (!rb_enc_asciicompat(enc)) {
        snprintf(q, qend-q, ".force_encoding(\"%s\")", enc->name);
        enc = rb_ascii8bit_encoding();
    }
    OBJ_INFECT_RAW(result, str);
    /* result from dump is ASCII */
    rb_enc_associate(result, enc);
    ENC_CODERANGE_SET(result, ENC_CODERANGE_7BIT);
    return result;
}


static void
rb_str_check_dummy_enc(rb_encoding *enc)
{
    if (rb_enc_dummy_p(enc)) {
        rb_raise(rb_eEncCompatError, "incompatible encoding with this operation: %s",
                 rb_enc_name(enc));
    }
}

/*
 *  call-seq:
 *     str.upcase!   -> str or nil
 *
 *  Upcases the contents of <i>str</i>, returning <code>nil</code> if no changes
 *  were made.
 *  Note: case replacement is effective only in ASCII region.
 */

static VALUE
rb_str_upcase_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *send;
    int modify = 0;
    int n;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    rb_str_check_dummy_enc(enc);
    s = RSTRING_PTR(str); send = RSTRING_END(str);
    if (single_byte_optimizable(str)) {
        while (s < send) {
            unsigned int c = *(unsigned char*)s;

            if (rb_enc_isascii(c, enc) && 'a' <= c && c <= 'z') {
                *s = 'A' + (c - 'a');
                modify = 1;
            }
            s++;
        }
    }
    else {
        int ascompat = rb_enc_asciicompat(enc);

        while (s < send) {
            unsigned int c;

            if (ascompat && (c = *(unsigned char*)s) < 0x80) {
                if (rb_enc_isascii(c, enc) && 'a' <= c && c <= 'z') {
                    *s = 'A' + (c - 'a');
                    modify = 1;
                }
                s++;
            }
            else {
                c = rb_enc_codepoint_len(s, send, &n, enc);
                if (rb_enc_islower(c, enc)) {
                    /* assuming toupper returns codepoint with same size */
                    rb_enc_mbcput(rb_enc_toupper(c, enc), s, enc);
                    modify = 1;
                }
                s += n;
            }
        }
    }

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.upcase   -> new_str
 *
 *  Returns a copy of <i>str</i> with all lowercase letters replaced with their
 *  uppercase counterparts. The operation is locale insensitive---only
 *  characters ``a'' to ``z'' are affected.
 *  Note: case replacement is effective only in ASCII region.
 *
 *     "hEllO".upcase   #=> "HELLO"
 */

static VALUE
rb_str_upcase(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_upcase_bang(str);
    return str;
}


/*
 *  call-seq:
 *     str.downcase!   -> str or nil
 *
 *  Downcases the contents of <i>str</i>, returning <code>nil</code> if no
 *  changes were made.
 *  Note: case replacement is effective only in ASCII region.
 */

static VALUE
rb_str_downcase_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *send;
    int modify = 0;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    rb_str_check_dummy_enc(enc);
    s = RSTRING_PTR(str); send = RSTRING_END(str);
    if (single_byte_optimizable(str)) {
        while (s < send) {
            unsigned int c = *(unsigned char*)s;

            if (rb_enc_isascii(c, enc) && 'A' <= c && c <= 'Z') {
                *s = 'a' + (c - 'A');
                modify = 1;
            }
            s++;
        }
    }
    else {
        int ascompat = rb_enc_asciicompat(enc);

        while (s < send) {
            unsigned int c;
            int n;

            if (ascompat && (c = *(unsigned char*)s) < 0x80) {
                if (rb_enc_isascii(c, enc) && 'A' <= c && c <= 'Z') {
                    *s = 'a' + (c - 'A');
                    modify = 1;
                }
                s++;
            }
            else {
                c = rb_enc_codepoint_len(s, send, &n, enc);
                if (rb_enc_isupper(c, enc)) {
                    /* assuming toupper returns codepoint with same size */
                    rb_enc_mbcput(rb_enc_tolower(c, enc), s, enc);
                    modify = 1;
                }
                s += n;
            }
        }
    }

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.downcase   -> new_str
 *
 *  Returns a copy of <i>str</i> with all uppercase letters replaced with their
 *  lowercase counterparts. The operation is locale insensitive---only
 *  characters ``A'' to ``Z'' are affected.
 *  Note: case replacement is effective only in ASCII region.
 *
 *     "hEllO".downcase   #=> "hello"
 */

static VALUE
rb_str_downcase(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_downcase_bang(str);
    return str;
}


/*
 *  call-seq:
 *     str.capitalize!   -> str or nil
 *
 *  Modifies <i>str</i> by converting the first character to uppercase and the
 *  remainder to lowercase. Returns <code>nil</code> if no changes are made.
 *  Note: case conversion is effective only in ASCII region.
 *
 *     a = "hello"
 *     a.capitalize!   #=> "Hello"
 *     a               #=> "Hello"
 *     a.capitalize!   #=> nil
 */

static VALUE
rb_str_capitalize_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *send;
    int modify = 0;
    unsigned int c;
    int n;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    rb_str_check_dummy_enc(enc);
    if (RSTRING_LEN(str) == 0 || !RSTRING_PTR(str)) return Qnil;
    s = RSTRING_PTR(str); send = RSTRING_END(str);

    c = rb_enc_codepoint_len(s, send, &n, enc);
    if (rb_enc_islower(c, enc)) {
        rb_enc_mbcput(rb_enc_toupper(c, enc), s, enc);
        modify = 1;
    }
    s += n;
    while (s < send) {
        c = rb_enc_codepoint_len(s, send, &n, enc);
        if (rb_enc_isupper(c, enc)) {
            rb_enc_mbcput(rb_enc_tolower(c, enc), s, enc);
            modify = 1;
        }
        s += n;
    }

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.capitalize   -> new_str
 *
 *  Returns a copy of <i>str</i> with the first character converted to uppercase
 *  and the remainder to lowercase.
 *  Note: case conversion is effective only in ASCII region.
 *
 *     "hello".capitalize    #=> "Hello"
 *     "HELLO".capitalize    #=> "Hello"
 *     "123ABC".capitalize   #=> "123abc"
 */

static VALUE
rb_str_capitalize(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_capitalize_bang(str);
    return str;
}


/*
 *  call-seq:
 *     str.swapcase!   -> str or nil
 *
 *  Equivalent to <code>String#swapcase</code>, but modifies the receiver in
 *  place, returning <i>str</i>, or <code>nil</code> if no changes were made.
 *  Note: case conversion is effective only in ASCII region.
 */

static VALUE
rb_str_swapcase_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *send;
    int modify = 0;
    int n;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    rb_str_check_dummy_enc(enc);
    s = RSTRING_PTR(str); send = RSTRING_END(str);
    while (s < send) {
        unsigned int c = rb_enc_codepoint_len(s, send, &n, enc);

        if (rb_enc_isupper(c, enc)) {
            /* assuming toupper returns codepoint with same size */
            rb_enc_mbcput(rb_enc_tolower(c, enc), s, enc);
            modify = 1;
        }
        else if (rb_enc_islower(c, enc)) {
            /* assuming tolower returns codepoint with same size */
            rb_enc_mbcput(rb_enc_toupper(c, enc), s, enc);
            modify = 1;
        }
        s += n;
    }

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.swapcase   -> new_str
 *
 *  Returns a copy of <i>str</i> with uppercase alphabetic characters converted
 *  to lowercase and lowercase characters converted to uppercase.
 *  Note: case conversion is effective only in ASCII region.
 *
 *     "Hello".swapcase          #=> "hELLO"
 *     "cYbEr_PuNk11".swapcase   #=> "CyBeR_pUnK11"
 */

static VALUE
rb_str_swapcase(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_swapcase_bang(str);
    return str;
}

typedef unsigned char *USTR;

struct tr {
    int gen;
    unsigned int now, max;
    char *p, *pend;
};

static unsigned int
trnext(struct tr *t, rb_encoding *enc)
{
    int n;

    for (;;) {
        if (!t->gen) {
nextpart:
            if (t->p == t->pend) return -1;
            if (rb_enc_ascget(t->p, t->pend, &n, enc) == '\\' && t->p + n < t->pend) {
                t->p += n;
            }
            t->now = rb_enc_codepoint_len(t->p, t->pend, &n, enc);
            t->p += n;
            if (rb_enc_ascget(t->p, t->pend, &n, enc) == '-' && t->p + n < t->pend) {
                t->p += n;
                if (t->p < t->pend) {
                    unsigned int c = rb_enc_codepoint_len(t->p, t->pend, &n, enc);
                    t->p += n;
                    if (t->now > c) {
                        if (t->now < 0x80 && c < 0x80) {
                            rb_raise(rb_eArgError,
                                     "invalid range \"%c-%c\" in string transliteration",
                                     t->now, c);
                        }
                        else {
                            rb_raise(rb_eArgError, "invalid range in string transliteration");
                        }
                        continue; /* not reached */
                    }
                    t->gen = 1;
                    t->max = c;
                }
            }
            return t->now;
        }
        else {
            while (ONIGENC_CODE_TO_MBCLEN(enc, ++t->now) <= 0) {
                if (t->now == t->max) {
                    t->gen = 0;
                    goto nextpart;
                }
            }
            if (t->now < t->max) {
                return t->now;
            }
            else {
                t->gen = 0;
                return t->max;
            }
        }
    }
}

static VALUE rb_str_delete_bang(int,VALUE*,VALUE);

static VALUE
tr_trans(VALUE str, VALUE src, VALUE repl, int sflag)
{
    const unsigned int errc = -1;
    unsigned int trans[256];
    rb_encoding *enc, *e1, *e2;
    struct tr trsrc, trrepl;
    int cflag = 0;
    unsigned int c, c0, last = 0;
    int modify = 0, i, l;
    char *s, *send;
    VALUE hash = 0;
    int singlebyte = single_byte_optimizable(str);
    int cr;

#define CHECK_IF_ASCII(c) \
    (void)((cr == ENC_CODERANGE_7BIT && !rb_isascii(c)) ? \
           (cr = ENC_CODERANGE_VALID) : 0)

    StringValue(src);
    StringValue(repl);
    if (RSTRING_LEN(str) == 0 || !RSTRING_PTR(str)) return Qnil;
    if (RSTRING_LEN(repl) == 0) {
        return rb_str_delete_bang(1, &src, str);
    }

    cr = ENC_CODERANGE(str);
    e1 = rb_enc_check(str, src);
    e2 = rb_enc_check(str, repl);
    if (e1 == e2) {
        enc = e1;
    }
    else {
        enc = rb_enc_check(src, repl);
    }
    trsrc.p = RSTRING_PTR(src); trsrc.pend = trsrc.p + RSTRING_LEN(src);
    if (RSTRING_LEN(src) > 1 &&
        rb_enc_ascget(trsrc.p, trsrc.pend, &l, enc) == '^' &&
        trsrc.p + l < trsrc.pend) {
        cflag = 1;
        trsrc.p += l;
    }
    trrepl.p = RSTRING_PTR(repl);
    trrepl.pend = trrepl.p + RSTRING_LEN(repl);
    trsrc.gen = trrepl.gen = 0;
    trsrc.now = trrepl.now = 0;
    trsrc.max = trrepl.max = 0;

    if (cflag) {
        for (i=0; i<256; i++) {
            trans[i] = 1;
        }
        while ((c = trnext(&trsrc, enc)) != errc) {
            if (c < 256) {
                trans[c] = errc;
            }
            else {
                if (!hash) hash = rb_hash_new();
                rb_hash_aset(hash, UINT2NUM(c), Qtrue);
            }
        }
        while ((c = trnext(&trrepl, enc)) != errc)
            /* retrieve last replacer */;
        last = trrepl.now;
        for (i=0; i<256; i++) {
            if (trans[i] != errc) {
                trans[i] = last;
            }
        }
    }
    else {
        unsigned int r;

        for (i=0; i<256; i++) {
            trans[i] = errc;
        }
        while ((c = trnext(&trsrc, enc)) != errc) {
            r = trnext(&trrepl, enc);
            if (r == errc) r = trrepl.now;
            if (c < 256) {
                trans[c] = r;
                if (rb_enc_codelen(r, enc) != 1) singlebyte = 0;
            }
            else {
                if (!hash) hash = rb_hash_new();
                rb_hash_aset(hash, UINT2NUM(c), UINT2NUM(r));
            }
        }
    }

    if (cr == ENC_CODERANGE_VALID)
        cr = ENC_CODERANGE_7BIT;
    str_modify_keep_cr(str);
    s = RSTRING_PTR(str); send = RSTRING_END(str);
    if (sflag) {
        int clen, tlen;
        long offset, max = RSTRING_LEN(str);
        unsigned int save = -1;
        char *buf = ALLOC_N(char, max), *t = buf;

        while (s < send) {
            int may_modify = 0;

            c0 = c = rb_enc_codepoint_len(s, send, &clen, e1);
            tlen = enc == e1 ? clen : rb_enc_codelen(c, enc);

            s += clen;
            if (c < 256) {
                c = trans[c];
            }
            else if (hash) {
                VALUE tmp = rb_hash_lookup(hash, UINT2NUM(c));
                if (NIL_P(tmp)) {
                    if (cflag) c = last;
                    else c = errc;
                }
                else if (cflag) c = errc;
                else c = NUM2INT(tmp);
            }
            else {
                c = errc;
            }
            if (c != (unsigned int)-1) {
                if (save == c) {
                    CHECK_IF_ASCII(c);
                    continue;
                }
                save = c;
                tlen = rb_enc_codelen(c, enc);
                modify = 1;
            }
            else {
                save = -1;
                c = c0;
                if (enc != e1) may_modify = 1;
            }
            while (t - buf + tlen >= max) {
                offset = t - buf;
                max *= 2;
                REALLOC_N(buf, char, max);
                t = buf + offset;
            }
            rb_enc_mbcput(c, t, enc);
            if (may_modify && memcmp(s, t, tlen) != 0) {
                modify = 1;
            }
            CHECK_IF_ASCII(c);
            t += tlen;
        }
        if (!STR_EMBED_P(str)) {
            ruby_sized_xfree(STR_HEAP_PTR(str), STR_HEAP_SIZE(str));
        }
        *t = '\0';
        RSTRING(str)->as.heap.ptr = buf;
        RSTRING(str)->as.heap.len = t - buf;
        STR_SET_NOEMBED(str);
        RSTRING(str)->as.heap.aux.capa = max;
    }
    else if (rb_enc_mbmaxlen(enc) == 1 || (singlebyte && !hash)) {
        while (s < send) {
            c = (unsigned char)*s;
            if (trans[c] != errc) {
                if (!cflag) {
                    c = trans[c];
                    *s = c;
                    modify = 1;
                }
                else {
                    *s = last;
                    modify = 1;
                }
            }
            CHECK_IF_ASCII(c);
            s++;
        }
    }
    else {
        int clen, tlen, max = (int)(RSTRING_LEN(str) * 1.2);
        long offset;
        char *buf = ALLOC_N(char, max), *t = buf;

        while (s < send) {
            int may_modify = 0;
            c0 = c = rb_enc_codepoint_len(s, send, &clen, e1);
            tlen = enc == e1 ? clen : rb_enc_codelen(c, enc);

            if (c < 256) {
                c = trans[c];
            }
            else if (hash) {
                VALUE tmp = rb_hash_lookup(hash, UINT2NUM(c));
                if (NIL_P(tmp)) {
                    if (cflag) c = last;
                    else c = errc;
                }
                else if (cflag) c = errc;
                else c = NUM2INT(tmp);
            }
            else {
                c = cflag ? last : errc;
            }
            if (c != errc) {
                tlen = rb_enc_codelen(c, enc);
                modify = 1;
            }
            else {
                c = c0;
                if (enc != e1) may_modify = 1;
            }
            while (t - buf + tlen >= max) {
                offset = t - buf;
                max *= 2;
                REALLOC_N(buf, char, max);
                t = buf + offset;
            }
            if (s != t) {
                rb_enc_mbcput(c, t, enc);
                if (may_modify && memcmp(s, t, tlen) != 0) {
                    modify = 1;
                }
            }
            CHECK_IF_ASCII(c);
            s += clen;
            t += tlen;
        }
        if (!STR_EMBED_P(str)) {
            ruby_sized_xfree(STR_HEAP_PTR(str), STR_HEAP_SIZE(str));
        }
        *t = '\0';
        RSTRING(str)->as.heap.ptr = buf;
        RSTRING(str)->as.heap.len = t - buf;
        STR_SET_NOEMBED(str);
        RSTRING(str)->as.heap.aux.capa = max;
    }

    if (modify) {
        if (cr != ENC_CODERANGE_BROKEN)
            ENC_CODERANGE_SET(str, cr);
        rb_enc_associate(str, enc);
        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.tr!(from_str, to_str)   -> str or nil
 *
 *  Translates <i>str</i> in place, using the same rules as
 *  <code>String#tr</code>. Returns <i>str</i>, or <code>nil</code> if no
 *  changes were made.
 */

static VALUE
rb_str_tr_bang(VALUE str, VALUE src, VALUE repl)
{
    return tr_trans(str, src, repl, 0);
}


/*
 *  call-seq:
 *     str.tr(from_str, to_str)   => new_str
 *
 *  Returns a copy of +str+ with the characters in +from_str+ replaced by the
 *  corresponding characters in +to_str+.  If +to_str+ is shorter than
 *  +from_str+, it is padded with its last character in order to maintain the
 *  correspondence.
 *
 *     "hello".tr('el', 'ip')      #=> "hippo"
 *     "hello".tr('aeiou', '*')    #=> "h*ll*"
 *     "hello".tr('aeiou', 'AA*')  #=> "hAll*"
 *
 *  Both strings may use the <code>c1-c2</code> notation to denote ranges of
 *  characters, and +from_str+ may start with a <code>^</code>, which denotes
 *  all characters except those listed.
 *
 *     "hello".tr('a-y', 'b-z')    #=> "ifmmp"
 *     "hello".tr('^aeiou', '*')   #=> "*e**o"
 *
 *  The backslash character <code></code> can be used to escape
 *  <code>^</code> or <code>-</code> and is otherwise ignored unless it
 *  appears at the end of a range or the end of the +from_str+ or +to_str+:
 *
 *     "hello^world".tr("\\^aeiou", "*") #=> "h*ll**w*rld"
 *     "hello-world".tr("a\\-eo", "*")   #=> "h*ll**w*rld"
 *
 *     "hello\r\nworld".tr("\r", "")   #=> "hello\nworld"
 *     "hello\r\nworld".tr("\\r", "")  #=> "hello\r\nwold"
 *     "hello\r\nworld".tr("\\\r", "") #=> "hello\nworld"
 *
 *     "X['\\b']".tr("X\\", "")   #=> "['b']"
 *     "X['\\b']".tr("X-\\]", "") #=> "'b'"
 */

static VALUE
rb_str_tr(VALUE str, VALUE src, VALUE repl)
{
    str = rb_str_dup(str);
    tr_trans(str, src, repl, 0);
    return str;
}

#define TR_TABLE_SIZE 257
static void
tr_setup_table(VALUE str, char stable[TR_TABLE_SIZE], int first,
               VALUE *tablep, VALUE *ctablep, rb_encoding *enc)
{
    const unsigned int errc = -1;
    char buf[256];
    struct tr tr;
    unsigned int c;
    VALUE table = 0, ptable = 0;
    int i, l, cflag = 0;

    tr.p = RSTRING_PTR(str); tr.pend = tr.p + RSTRING_LEN(str);
    tr.gen = tr.now = tr.max = 0;

    if (RSTRING_LEN(str) > 1 && rb_enc_ascget(tr.p, tr.pend, &l, enc) == '^') {
        cflag = 1;
        tr.p += l;
    }
    if (first) {
        for (i=0; i<256; i++) {
            stable[i] = 1;
        }
        stable[256] = cflag;
    }
    else if (stable[256] && !cflag) {
        stable[256] = 0;
    }
    for (i=0; i<256; i++) {
        buf[i] = cflag;
    }

    while ((c = trnext(&tr, enc)) != errc) {
        if (c < 256) {
            buf[c & 0xff] = !cflag;
        }
        else {
            VALUE key = UINT2NUM(c);

            if (!table && (first || *tablep || stable[256])) {
                if (cflag) {
                    ptable = *ctablep;
                    table = ptable ? ptable : rb_hash_new();
                    *ctablep = table;
                }
                else {
                    table = rb_hash_new();
                    ptable = *tablep;
                    *tablep = table;
                }
            }
            if (table && (!ptable || (cflag ^ !NIL_P(rb_hash_aref(ptable, key))))) {
                rb_hash_aset(table, key, Qtrue);
            }
        }
    }
    for (i=0; i<256; i++) {
        stable[i] = stable[i] && buf[i];
    }
    if (!table && !cflag) {
        *tablep = 0;
    }
}


static int
tr_find(unsigned int c, const char table[TR_TABLE_SIZE], VALUE del, VALUE nodel)
{
    if (c < 256) {
        return table[c] != 0;
    }
    else {
        VALUE v = UINT2NUM(c);

        if (del) {
            if (!NIL_P(rb_hash_lookup(del, v)) &&
                    (!nodel || NIL_P(rb_hash_lookup(nodel, v)))) {
                return TRUE;
            }
        }
        else if (nodel && !NIL_P(rb_hash_lookup(nodel, v))) {
            return FALSE;
        }
        return table[256] ? TRUE : FALSE;
    }
}

/*
 *  call-seq:
 *     str.delete!([other_str]+)   -> str or nil
 *
 *  Performs a <code>delete</code> operation in place, returning <i>str</i>, or
 *  <code>nil</code> if <i>str</i> was not modified.
 */

static VALUE
rb_str_delete_bang(int argc, VALUE *argv, VALUE str)
{
    char squeez[TR_TABLE_SIZE];
    rb_encoding *enc = 0;
    char *s, *send, *t;
    VALUE del = 0, nodel = 0;
    int modify = 0;
    int i, ascompat, cr;

    if (RSTRING_LEN(str) == 0 || !RSTRING_PTR(str)) return Qnil;
    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    for (i=0; i<argc; i++) {
        VALUE s = argv[i];

        StringValue(s);
        enc = rb_enc_check(str, s);
        tr_setup_table(s, squeez, i==0, &del, &nodel, enc);
    }

    str_modify_keep_cr(str);
    ascompat = rb_enc_asciicompat(enc);
    s = t = RSTRING_PTR(str);
    send = RSTRING_END(str);
    cr = ascompat ? ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID;
    while (s < send) {
        unsigned int c;
        int clen;

        if (ascompat && (c = *(unsigned char*)s) < 0x80) {
            if (squeez[c]) {
                modify = 1;
            }
            else {
                if (t != s) *t = c;
                t++;
            }
            s++;
        }
        else {
            c = rb_enc_codepoint_len(s, send, &clen, enc);

            if (tr_find(c, squeez, del, nodel)) {
                modify = 1;
            }
            else {
                if (t != s) rb_enc_mbcput(c, t, enc);
                t += clen;
                if (cr == ENC_CODERANGE_7BIT) cr = ENC_CODERANGE_VALID;
            }
            s += clen;
        }
    }
    *t = '\0';
    STR_SET_LEN(str, t - RSTRING_PTR(str));
    ENC_CODERANGE_SET(str, cr);

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.delete([other_str]+)   -> new_str
 *
 *  Returns a copy of <i>str</i> with all characters in the intersection of its
 *  arguments deleted. Uses the same rules for building the set of characters as
 *  <code>String#count</code>.
 *
 *     "hello".delete "l","lo"        #=> "heo"
 *     "hello".delete "lo"            #=> "he"
 *     "hello".delete "aeiou", "^e"   #=> "hell"
 *     "hello".delete "ej-m"          #=> "ho"
 */

static VALUE
rb_str_delete(int argc, VALUE *argv, VALUE str)
{
    str = rb_str_dup(str);
    rb_str_delete_bang(argc, argv, str);
    return str;
}


/*
 *  call-seq:
 *     str.squeeze!([other_str]*)   -> str or nil
 *
 *  Squeezes <i>str</i> in place, returning either <i>str</i>, or
 *  <code>nil</code> if no changes were made.
 */

static VALUE
rb_str_squeeze_bang(int argc, VALUE *argv, VALUE str)
{
    char squeez[TR_TABLE_SIZE];
    rb_encoding *enc = 0;
    VALUE del = 0, nodel = 0;
    char *s, *send, *t;
    int i, modify = 0;
    int ascompat, singlebyte = single_byte_optimizable(str);
    unsigned int save;

    if (argc == 0) {
        enc = STR_ENC_GET(str);
    }
    else {
        for (i=0; i<argc; i++) {
            VALUE s = argv[i];

            StringValue(s);
            enc = rb_enc_check(str, s);
            if (singlebyte && !single_byte_optimizable(s))
                singlebyte = 0;
            tr_setup_table(s, squeez, i==0, &del, &nodel, enc);
        }
    }

    str_modify_keep_cr(str);
    s = t = RSTRING_PTR(str);
    if (!s || RSTRING_LEN(str) == 0) return Qnil;
    send = RSTRING_END(str);
    save = -1;
    ascompat = rb_enc_asciicompat(enc);

    if (singlebyte) {
        while (s < send) {
            unsigned int c = *(unsigned char*)s++;
            if (c != save || (argc > 0 && !squeez[c])) {
                *t++ = save = c;
            }
        }
    } else {
        while (s < send) {
            unsigned int c;
            int clen;

            if (ascompat && (c = *(unsigned char*)s) < 0x80) {
                if (c != save || (argc > 0 && !squeez[c])) {
                    *t++ = save = c;
                }
                s++;
            }
            else {
                c = rb_enc_codepoint_len(s, send, &clen, enc);

                if (c != save || (argc > 0 && !tr_find(c, squeez, del, nodel))) {
                    if (t != s) rb_enc_mbcput(c, t, enc);
                    save = c;
                    t += clen;
                }
                s += clen;
            }
        }
    }

    *t = '\0';
    if (t - RSTRING_PTR(str) != RSTRING_LEN(str)) {
        STR_SET_LEN(str, t - RSTRING_PTR(str));
        modify = 1;
    }

    if (modify) return str;
    return Qnil;
}


/*
 *  call-seq:
 *     str.squeeze([other_str]*)    -> new_str
 *
 *  Builds a set of characters from the <i>other_str</i> parameter(s) using the
 *  procedure described for <code>String#count</code>. Returns a new string
 *  where runs of the same character that occur in this set are replaced by a
 *  single character. If no arguments are given, all runs of identical
 *  characters are replaced by a single character.
 *
 *     "yellow moon".squeeze                  #=> "yelow mon"
 *     "  now   is  the".squeeze(" ")         #=> " now is the"
 *     "putters shoot balls".squeeze("m-z")   #=> "puters shot balls"
 */

static VALUE
rb_str_squeeze(int argc, VALUE *argv, VALUE str)
{
    str = rb_str_dup(str);
    rb_str_squeeze_bang(argc, argv, str);
    return str;
}


/*
 *  call-seq:
 *     str.tr_s!(from_str, to_str)   -> str or nil
 *
 *  Performs <code>String#tr_s</code> processing on <i>str</i> in place,
 *  returning <i>str</i>, or <code>nil</code> if no changes were made.
 */

static VALUE
rb_str_tr_s_bang(VALUE str, VALUE src, VALUE repl)
{
    return tr_trans(str, src, repl, 1);
}


/*
 *  call-seq:
 *     str.tr_s(from_str, to_str)   -> new_str
 *
 *  Processes a copy of <i>str</i> as described under <code>String#tr</code>,
 *  then removes duplicate characters in regions that were affected by the
 *  translation.
 *
 *     "hello".tr_s('l', 'r')     #=> "hero"
 *     "hello".tr_s('el', '*')    #=> "h*o"
 *     "hello".tr_s('el', 'hx')   #=> "hhxo"
 */

static VALUE
rb_str_tr_s(VALUE str, VALUE src, VALUE repl)
{
    str = rb_str_dup(str);
    tr_trans(str, src, repl, 1);
    return str;
}


/*
 *  call-seq:
 *     str.count([other_str]+)   -> fixnum
 *
 *  Each +other_str+ parameter defines a set of characters to count.  The
 *  intersection of these sets defines the characters to count in +str+.  Any
 *  +other_str+ that starts with a caret <code>^</code> is negated.  The
 *  sequence <code>c1-c2</code> means all characters between c1 and c2.  The
 *  backslash character <code></code> can be used to escape <code>^</code> or
 *  <code>-</code> and is otherwise ignored unless it appears at the end of a
 *  sequence or the end of a +other_str+.
 *
 *     a = "hello world"
 *     a.count "lo"                   #=> 5
 *     a.count "lo", "o"              #=> 2
 *     a.count "hello", "^l"          #=> 4
 *     a.count "ej-m"                 #=> 4
 *
 *     "hello^world".count "\\^aeiou" #=> 4
 *     "hello-world".count "a\\-eo"   #=> 4
 *
 *     c = "hello world\\r\\n"
 *     c.count "\\"                   #=> 2
 *     c.count "\\A"                  #=> 0
 *     c.count "X-\\w"                #=> 3
 */

static VALUE
rb_str_count(int argc, VALUE *argv, VALUE str)
{
    char table[TR_TABLE_SIZE];
    rb_encoding *enc = 0;
    VALUE del = 0, nodel = 0, tstr;
    char *s, *send;
    int i;
    int ascompat;

    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);

    tstr = argv[0];
    StringValue(tstr);
    enc = rb_enc_check(str, tstr);
    if (argc == 1) {
        const char *ptstr;
        if (RSTRING_LEN(tstr) == 1 && rb_enc_asciicompat(enc) &&
            (ptstr = RSTRING_PTR(tstr),
             ONIGENC_IS_ALLOWED_REVERSE_MATCH(enc, (const unsigned char *)ptstr, (const unsigned char *)ptstr+1)) &&
            !is_broken_string(str)) {
            int n = 0;
            int clen;
            unsigned char c = rb_enc_codepoint_len(ptstr, ptstr+1, &clen, enc);

            s = RSTRING_PTR(str);
            if (!s || RSTRING_LEN(str) == 0) return INT2FIX(0);
            send = RSTRING_END(str);
            while (s < send) {
                if (*(unsigned char*)s++ == c) n++;
            }
            return INT2NUM(n);
        }
    }

    tr_setup_table(tstr, table, TRUE, &del, &nodel, enc);
    for (i=1; i<argc; i++) {
        tstr = argv[i];
        StringValue(tstr);
        enc = rb_enc_check(str, tstr);
        tr_setup_table(tstr, table, FALSE, &del, &nodel, enc);
    }

    s = RSTRING_PTR(str);
    if (!s || RSTRING_LEN(str) == 0) return INT2FIX(0);
    send = RSTRING_END(str);
    ascompat = rb_enc_asciicompat(enc);
    i = 0;
    while (s < send) {
        unsigned int c;

        if (ascompat && (c = *(unsigned char*)s) < 0x80) {
            if (table[c]) {
                i++;
            }
            s++;
        }
        else {
            int clen;
            c = rb_enc_codepoint_len(s, send, &clen, enc);
            if (tr_find(c, table, del, nodel)) {
                i++;
            }
            s += clen;
        }
    }

    return INT2NUM(i);
}

static const char isspacetable[256] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

#define ascii_isspace(c) isspacetable[(unsigned char)(c)]

/*
 *  call-seq:
 *     str.split(pattern=$;, [limit])   -> anArray
 *
 *  Divides <i>str</i> into substrings based on a delimiter, returning an array
 *  of these substrings.
 *
 *  If <i>pattern</i> is a <code>String</code>, then its contents are used as
 *  the delimiter when splitting <i>str</i>. If <i>pattern</i> is a single
 *  space, <i>str</i> is split on whitespace, with leading whitespace and runs
 *  of contiguous whitespace characters ignored.
 *
 *  If <i>pattern</i> is a <code>Regexp</code>, <i>str</i> is divided where the
 *  pattern matches. Whenever the pattern matches a zero-length string,
 *  <i>str</i> is split into individual characters. If <i>pattern</i> contains
 *  groups, the respective matches will be returned in the array as well.
 *
 *  If <i>pattern</i> is omitted, the value of <code>$;</code> is used.  If
 *  <code>$;</code> is <code>nil</code> (which is the default), <i>str</i> is
 *  split on whitespace as if ` ' were specified.
 *
 *  If the <i>limit</i> parameter is omitted, trailing null fields are
 *  suppressed. If <i>limit</i> is a positive number, at most that number of
 *  fields will be returned (if <i>limit</i> is <code>1</code>, the entire
 *  string is returned as the only entry in an array). If negative, there is no
 *  limit to the number of fields returned, and trailing null fields are not
 *  suppressed.
 *
 *  When the input +str+ is empty an empty Array is returned as the string is
 *  considered to have no fields to split.
 *
 *     " now's  the time".split        #=> ["now's", "the", "time"]
 *     " now's  the time".split(' ')   #=> ["now's", "the", "time"]
 *     " now's  the time".split(/ /)   #=> ["", "now's", "", "the", "time"]
 *     "1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]
 *     "hello".split(//)               #=> ["h", "e", "l", "l", "o"]
 *     "hello".split(//, 3)            #=> ["h", "e", "llo"]
 *     "hi mom".split(%r{\s*})         #=> ["h", "i", "m", "o", "m"]
 *
 *     "mellow yellow".split("ello")   #=> ["m", "w y", "w"]
 *     "1,2,,3,4,,".split(',')         #=> ["1", "2", "", "3", "4"]
 *     "1,2,,3,4,,".split(',', 4)      #=> ["1", "2", "", "3,4,,"]
 *     "1,2,,3,4,,".split(',', -4)     #=> ["1", "2", "", "3", "4", "", ""]
 *
 *     "".split(',', -1)               #=> []
 */

static VALUE
rb_str_split_m(int argc, VALUE *argv, VALUE str)
{
    rb_encoding *enc;
    VALUE spat;
    VALUE limit;
    enum {awk, string, regexp} split_type;
    long beg, end, i = 0;
    int lim = 0;
    VALUE result, tmp;

    if (rb_scan_args(argc, argv, "02", &spat, &limit) == 2) {
        lim = NUM2INT(limit);
        if (lim <= 0) limit = Qnil;
        else if (lim == 1) {
            if (RSTRING_LEN(str) == 0)
                return rb_ary_new2(0);
            return rb_ary_new3(1, str);
        }
        i = 1;
    }

    enc = STR_ENC_GET(str);
    if (NIL_P(spat) && NIL_P(spat = rb_fs)) {
        split_type = awk;
    }
    else {
        if (RB_TYPE_P(spat, T_STRING)) {
            rb_encoding *enc2 = STR_ENC_GET(spat);

            split_type = string;
            if (RSTRING_LEN(spat) == 0) {
                /* Special case - split into chars */
                spat = rb_reg_regcomp(spat);
                split_type = regexp;
            }
            else if (rb_enc_asciicompat(enc2) == 1) {
                if (RSTRING_LEN(spat) == 1 && RSTRING_PTR(spat)[0] == ' '){
                    split_type = awk;
                }
            }
            else {
                int l;
                if (rb_enc_ascget(RSTRING_PTR(spat), RSTRING_END(spat), &l, enc2) == ' ' &&
                    RSTRING_LEN(spat) == l) {
                    split_type = awk;
                }
            }
        }
        else {
            spat = get_pat(spat, 1);
            split_type = regexp;
        }
    }

    result = rb_ary_new();
    beg = 0;
    if (split_type == awk) {
        char *ptr = RSTRING_PTR(str);
        char *eptr = RSTRING_END(str);
        char *bptr = ptr;
        int skip = 1;
        unsigned int c;

        end = beg;
        if (is_ascii_string(str)) {
            while (ptr < eptr) {
                c = (unsigned char)*ptr++;
                if (skip) {
                    if (ascii_isspace(c)) {
                        beg = ptr - bptr;
                    }
                    else {
                        end = ptr - bptr;
                        skip = 0;
                        if (!NIL_P(limit) && lim <= i) break;
                    }
                }
                else if (ascii_isspace(c)) {
                    rb_ary_push(result, rb_str_subseq(str, beg, end-beg));
                    skip = 1;
                    beg = ptr - bptr;
                    if (!NIL_P(limit)) ++i;
                }
                else {
                    end = ptr - bptr;
                }
            }
        }
        else {
            while (ptr < eptr) {
                int n;

                c = rb_enc_codepoint_len(ptr, eptr, &n, enc);
                ptr += n;
                if (skip) {
                    if (rb_isspace(c)) {
                        beg = ptr - bptr;
                    }
                    else {
                        end = ptr - bptr;
                        skip = 0;
                        if (!NIL_P(limit) && lim <= i) break;
                    }
                }
                else if (rb_isspace(c)) {
                    rb_ary_push(result, rb_str_subseq(str, beg, end-beg));
                    skip = 1;
                    beg = ptr - bptr;
                    if (!NIL_P(limit)) ++i;
                }
                else {
                    end = ptr - bptr;
                }
            }
        }
    }
    else if (split_type == string) {
        char *ptr = RSTRING_PTR(str);
        char *temp = ptr;
        char *eptr = RSTRING_END(str);
        char *sptr = RSTRING_PTR(spat);
        long slen = RSTRING_LEN(spat);

        if (is_broken_string(str)) {
            rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(STR_ENC_GET(str)));
        }
        if (is_broken_string(spat)) {
            rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(STR_ENC_GET(spat)));
        }
        enc = rb_enc_check(str, spat);
        while (ptr < eptr &&
               (end = rb_memsearch(sptr, slen, ptr, eptr - ptr, enc)) >= 0) {
            /* Check we are at the start of a char */
            char *t = rb_enc_right_char_head(ptr, ptr + end, eptr, enc);
            if (t != ptr + end) {
                ptr = t;
                continue;
            }
            rb_ary_push(result, rb_str_subseq(str, ptr - temp, end));
            ptr += end + slen;
            if (!NIL_P(limit) && lim <= ++i) break;
        }
        beg = ptr - temp;
    }
    else {
        char *ptr = RSTRING_PTR(str);
        long len = RSTRING_LEN(str);
        long start = beg;
        long idx;
        int last_null = 0;
        struct re_registers *regs;

        while ((end = rb_reg_search(spat, str, start, 0)) >= 0) {
            regs = RMATCH_REGS(rb_backref_get());
            if (start == end && BEG(0) == END(0)) {
                if (!ptr) {
                    rb_ary_push(result, str_new_empty(str));
                    break;
                }
                else if (last_null == 1) {
                    rb_ary_push(result, rb_str_subseq(str, beg,
                                                      rb_enc_fast_mbclen(ptr+beg,
                                                                         ptr+len,
                                                                         enc)));
                    beg = start;
                }
                else {
                    if (ptr+start == ptr+len)
                        start++;
                    else
                        start += rb_enc_fast_mbclen(ptr+start,ptr+len,enc);
                    last_null = 1;
                    continue;
                }
            }
            else {
                rb_ary_push(result, rb_str_subseq(str, beg, end-beg));
                beg = start = END(0);
            }
            last_null = 0;

            for (idx=1; idx < regs->num_regs; idx++) {
                if (BEG(idx) == -1) continue;
                if (BEG(idx) == END(idx))
                    tmp = str_new_empty(str);
                else
                    tmp = rb_str_subseq(str, BEG(idx), END(idx)-BEG(idx));
                rb_ary_push(result, tmp);
            }
            if (!NIL_P(limit) && lim <= ++i) break;
        }
    }
    if (RSTRING_LEN(str) > 0 && (!NIL_P(limit) || RSTRING_LEN(str) > beg || lim < 0)) {
        if (RSTRING_LEN(str) == beg)
            tmp = str_new_empty(str);
        else
            tmp = rb_str_subseq(str, beg, RSTRING_LEN(str)-beg);
        rb_ary_push(result, tmp);
    }
    if (NIL_P(limit) && lim == 0) {
        long len;
        while ((len = RARRAY_LEN(result)) > 0 &&
               (tmp = RARRAY_AREF(result, len-1), RSTRING_LEN(tmp) == 0))
            rb_ary_pop(result);
    }

    return result;
}

VALUE
rb_str_split(VALUE str, const char *sep0)
{
    VALUE sep;

    StringValue(str);
    sep = rb_str_new2(sep0);
    return rb_str_split_m(1, &sep, str);
}


static VALUE
rb_str_enumerate_lines(int argc, VALUE *argv, VALUE str, int wantarray)
{
    rb_encoding *enc;
    VALUE line, rs, orig = str;
    const char *ptr, *pend, *subptr, *subend, *rsptr, *hit, *adjusted;
    long pos, len, rslen;
    int paragraph_mode = 0;

    VALUE UNINITIALIZED_VAR(ary);

    if (argc == 0)
        rs = rb_rs;
    else
        rb_scan_args(argc, argv, "01", &rs);

    if (rb_block_given_p()) {
        if (wantarray) {
#if STRING_ENUMERATORS_WANTARRAY
            rb_warn("given block not used");
            ary = rb_ary_new();
#else
            rb_warning("passing a block to String#lines is deprecated");
            wantarray = 0;
#endif
        }
    }
    else {
        if (wantarray)
            ary = rb_ary_new();
        else
            RETURN_ENUMERATOR(str, argc, argv);
    }

    if (NIL_P(rs)) {
        if (wantarray) {
            rb_ary_push(ary, str);
            return ary;
        }
        else {
            rb_yield(str);
            return orig;
        }
    }

    str = rb_str_new4(str);
    ptr = subptr = RSTRING_PTR(str);
    pend = RSTRING_END(str);
    len = RSTRING_LEN(str);
    StringValue(rs);
    rslen = RSTRING_LEN(rs);

    if (rs == rb_default_rs)
        enc = rb_enc_get(str);
    else
        enc = rb_enc_check(str, rs);

    if (rslen == 0) {
        rsptr = "\n\n";
        rslen = 2;
        paragraph_mode = 1;
    }
    else {
        rsptr = RSTRING_PTR(rs);
    }

    if ((rs == rb_default_rs || paragraph_mode) && !rb_enc_asciicompat(enc)) {
        rs = rb_str_new(rsptr, rslen);
        rs = rb_str_encode(rs, rb_enc_from_encoding(enc), 0, Qnil);
        rsptr = RSTRING_PTR(rs);
        rslen = RSTRING_LEN(rs);
    }

    while (subptr < pend) {
        pos = rb_memsearch(rsptr, rslen, subptr, pend - subptr, enc);
        if (pos < 0) break;
        hit = subptr + pos;
        adjusted = rb_enc_right_char_head(subptr, hit, pend, enc);
        if (hit != adjusted) {
            subptr = adjusted;
            continue;
        }
        subend = hit + rslen;
        if (paragraph_mode) {
            while (subend < pend && rb_enc_is_newline(subend, pend, enc)) {
                subend += rb_enc_mbclen(subend, pend, enc);
            }
        }
        line = rb_str_subseq(str, subptr - ptr, subend - subptr);
        if (wantarray) {
            rb_ary_push(ary, line);
        }
        else {
            rb_yield(line);
            str_mod_check(str, ptr, len);
        }
        subptr = subend;
    }

    if (subptr != pend) {
        line = rb_str_subseq(str, subptr - ptr, pend - subptr);
        if (wantarray)
            rb_ary_push(ary, line);
        else
            rb_yield(line);
        RB_GC_GUARD(str);
    }

    if (wantarray)
        return ary;
    else
        return orig;
}

/*
 *  call-seq:
 *     str.each_line(separator=$/) {|substr| block }   -> str
 *     str.each_line(separator=$/)                     -> an_enumerator
 *
 *  Splits <i>str</i> using the supplied parameter as the record
 *  separator (<code>$/</code> by default), passing each substring in
 *  turn to the supplied block.  If a zero-length record separator is
 *  supplied, the string is split into paragraphs delimited by
 *  multiple successive newlines.
 *
 *  If no block is given, an enumerator is returned instead.
 *
 *     print "Example one\n"
 *     "hello\nworld".each_line {|s| p s}
 *     print "Example two\n"
 *     "hello\nworld".each_line('l') {|s| p s}
 *     print "Example three\n"
 *     "hello\n\n\nworld".each_line('') {|s| p s}
 *
 *  <em>produces:</em>
 *
 *     Example one
 *     "hello\n"
 *     "world"
 *     Example two
 *     "hel"
 *     "l"
 *     "o\nworl"
 *     "d"
 *     Example three
 *     "hello\n\n\n"
 *     "world"
 */

static VALUE
rb_str_each_line(int argc, VALUE *argv, VALUE str)
{
    return rb_str_enumerate_lines(argc, argv, str, 0);
}

/*
 *  call-seq:
 *     str.lines(separator=$/)  -> an_array
 *
 *  Returns an array of lines in <i>str</i> split using the supplied
 *  record separator (<code>$/</code> by default).  This is a
 *  shorthand for <code>str.each_line(separator).to_a</code>.
 *
 *  If a block is given, which is a deprecated form, works the same as
 *  <code>each_line</code>.
 */

static VALUE
rb_str_lines(int argc, VALUE *argv, VALUE str)
{
    return rb_str_enumerate_lines(argc, argv, str, 1);
}

static VALUE
rb_str_each_byte_size(VALUE str, VALUE args, VALUE eobj)
{
    return LONG2FIX(RSTRING_LEN(str));
}

static VALUE
rb_str_enumerate_bytes(VALUE str, int wantarray)
{
    long i;
    VALUE UNINITIALIZED_VAR(ary);

    if (rb_block_given_p()) {
        if (wantarray) {
#if STRING_ENUMERATORS_WANTARRAY
            rb_warn("given block not used");
            ary = rb_ary_new();
#else
            rb_warning("passing a block to String#bytes is deprecated");
            wantarray = 0;
#endif
        }
    }
    else {
        if (wantarray)
            ary = rb_ary_new2(RSTRING_LEN(str));
        else
            RETURN_SIZED_ENUMERATOR(str, 0, 0, rb_str_each_byte_size);
    }

    for (i=0; i<RSTRING_LEN(str); i++) {
        if (wantarray)
            rb_ary_push(ary, INT2FIX(RSTRING_PTR(str)[i] & 0xff));
        else
            rb_yield(INT2FIX(RSTRING_PTR(str)[i] & 0xff));
    }
    if (wantarray)
        return ary;
    else
        return str;
}

/*
 *  call-seq:
 *     str.each_byte {|fixnum| block }    -> str
 *     str.each_byte                      -> an_enumerator
 *
 *  Passes each byte in <i>str</i> to the given block, or returns an
 *  enumerator if no block is given.
 *
 *     "hello".each_byte {|c| print c, ' ' }
 *
 *  <em>produces:</em>
 *
 *     104 101 108 108 111
 */

static VALUE
rb_str_each_byte(VALUE str)
{
    return rb_str_enumerate_bytes(str, 0);
}

/*
 *  call-seq:
 *     str.bytes    -> an_array
 *
 *  Returns an array of bytes in <i>str</i>.  This is a shorthand for
 *  <code>str.each_byte.to_a</code>.
 *
 *  If a block is given, which is a deprecated form, works the same as
 *  <code>each_byte</code>.
 */

static VALUE
rb_str_bytes(VALUE str)
{
    return rb_str_enumerate_bytes(str, 1);
}

static VALUE
rb_str_each_char_size(VALUE str, VALUE args, VALUE eobj)
{
    return rb_str_length(str);
}

static VALUE
rb_str_enumerate_chars(VALUE str, int wantarray)
{
    VALUE orig = str;
    VALUE substr;
    long i, len, n;
    const char *ptr;
    rb_encoding *enc;
    VALUE UNINITIALIZED_VAR(ary);

    str = rb_str_new4(str);
    ptr = RSTRING_PTR(str);
    len = RSTRING_LEN(str);
    enc = rb_enc_get(str);

    if (rb_block_given_p()) {
        if (wantarray) {
#if STRING_ENUMERATORS_WANTARRAY
            rb_warn("given block not used");
            ary = rb_ary_new_capa(str_strlen(str, enc));
#else
            rb_warning("passing a block to String#chars is deprecated");
            wantarray = 0;
#endif
        }
    }
    else {
        if (wantarray)
            ary = rb_ary_new_capa(str_strlen(str, enc));
        else
            RETURN_SIZED_ENUMERATOR(str, 0, 0, rb_str_each_char_size);
    }

    switch (ENC_CODERANGE(str)) {
      case ENC_CODERANGE_VALID:
      case ENC_CODERANGE_7BIT:
        for (i = 0; i < len; i += n) {
            n = rb_enc_fast_mbclen(ptr + i, ptr + len, enc);
            substr = rb_str_subseq(str, i, n);
            if (wantarray)
                rb_ary_push(ary, substr);
            else
                rb_yield(substr);
        }
        break;
      default:
        for (i = 0; i < len; i += n) {
            n = rb_enc_mbclen(ptr + i, ptr + len, enc);
            substr = rb_str_subseq(str, i, n);
            if (wantarray)
                rb_ary_push(ary, substr);
            else
                rb_yield(substr);
        }
    }
    RB_GC_GUARD(str);
    if (wantarray)
        return ary;
    else
        return orig;
}

/*
 *  call-seq:
 *     str.each_char {|cstr| block }    -> str
 *     str.each_char                    -> an_enumerator
 *
 *  Passes each character in <i>str</i> to the given block, or returns
 *  an enumerator if no block is given.
 *
 *     "hello".each_char {|c| print c, ' ' }
 *
 *  <em>produces:</em>
 *
 *     h e l l o
 */

static VALUE
rb_str_each_char(VALUE str)
{
    return rb_str_enumerate_chars(str, 0);
}

/*
 *  call-seq:
 *     str.chars    -> an_array
 *
 *  Returns an array of characters in <i>str</i>.  This is a shorthand
 *  for <code>str.each_char.to_a</code>.
 *
 *  If a block is given, which is a deprecated form, works the same as
 *  <code>each_char</code>.
 */

static VALUE
rb_str_chars(VALUE str)
{
    return rb_str_enumerate_chars(str, 1);
}


static VALUE
rb_str_enumerate_codepoints(VALUE str, int wantarray)
{
    VALUE orig = str;
    int n;
    unsigned int c;
    const char *ptr, *end;
    rb_encoding *enc;
    VALUE UNINITIALIZED_VAR(ary);

    if (single_byte_optimizable(str))
        return rb_str_enumerate_bytes(str, wantarray);

    str = rb_str_new4(str);
    ptr = RSTRING_PTR(str);
    end = RSTRING_END(str);
    enc = STR_ENC_GET(str);

    if (rb_block_given_p()) {
        if (wantarray) {
#if STRING_ENUMERATORS_WANTARRAY
            rb_warn("given block not used");
            ary = rb_ary_new_capa(str_strlen(str, enc));
#else
            rb_warning("passing a block to String#codepoints is deprecated");
            wantarray = 0;
#endif
        }
    }
    else {
        if (wantarray)
            ary = rb_ary_new_capa(str_strlen(str, enc));
        else
            RETURN_SIZED_ENUMERATOR(str, 0, 0, rb_str_each_char_size);
    }

    while (ptr < end) {
        c = rb_enc_codepoint_len(ptr, end, &n, enc);
        if (wantarray)
            rb_ary_push(ary, UINT2NUM(c));
        else
            rb_yield(UINT2NUM(c));
        ptr += n;
    }
    RB_GC_GUARD(str);
    if (wantarray)
        return ary;
    else
        return orig;
}

/*
 *  call-seq:
 *     str.each_codepoint {|integer| block }    -> str
 *     str.each_codepoint                       -> an_enumerator
 *
 *  Passes the <code>Integer</code> ordinal of each character in <i>str</i>,
 *  also known as a <i>codepoint</i> when applied to Unicode strings to the
 *  given block.
 *
 *  If no block is given, an enumerator is returned instead.
 *
 *     "hello\u0639".each_codepoint {|c| print c, ' ' }
 *
 *  <em>produces:</em>
 *
 *     104 101 108 108 111 1593
 */

static VALUE
rb_str_each_codepoint(VALUE str)
{
    return rb_str_enumerate_codepoints(str, 0);
}

/*
 *  call-seq:
 *     str.codepoints   -> an_array
 *
 *  Returns an array of the <code>Integer</code> ordinals of the
 *  characters in <i>str</i>.  This is a shorthand for
 *  <code>str.each_codepoint.to_a</code>.
 *
 *  If a block is given, which is a deprecated form, works the same as
 *  <code>each_codepoint</code>.
 */

static VALUE
rb_str_codepoints(VALUE str)
{
    return rb_str_enumerate_codepoints(str, 1);
}


static long
chopped_length(VALUE str)
{
    rb_encoding *enc = STR_ENC_GET(str);
    const char *p, *p2, *beg, *end;

    beg = RSTRING_PTR(str);
    end = beg + RSTRING_LEN(str);
    if (beg > end) return 0;
    p = rb_enc_prev_char(beg, end, end, enc);
    if (!p) return 0;
    if (p > beg && rb_enc_ascget(p, end, 0, enc) == '\n') {
        p2 = rb_enc_prev_char(beg, p, end, enc);
        if (p2 && rb_enc_ascget(p2, end, 0, enc) == '\r') p = p2;
    }
    return p - beg;
}

/*
 *  call-seq:
 *     str.chop!   -> str or nil
 *
 *  Processes <i>str</i> as for <code>String#chop</code>, returning <i>str</i>,
 *  or <code>nil</code> if <i>str</i> is the empty string.  See also
 *  <code>String#chomp!</code>.
 */

static VALUE
rb_str_chop_bang(VALUE str)
{
    str_modify_keep_cr(str);
    if (RSTRING_LEN(str) > 0) {
        long len;
        len = chopped_length(str);
        STR_SET_LEN(str, len);
        RSTRING_PTR(str)[len] = '\0';
        if (ENC_CODERANGE(str) != ENC_CODERANGE_7BIT) {
            ENC_CODERANGE_CLEAR(str);
        }
        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.chop   -> new_str
 *
 *  Returns a new <code>String</code> with the last character removed.  If the
 *  string ends with <code>\r\n</code>, both characters are removed. Applying
 *  <code>chop</code> to an empty string returns an empty
 *  string. <code>String#chomp</code> is often a safer alternative, as it leaves
 *  the string unchanged if it doesn't end in a record separator.
 *
 *     "string\r\n".chop   #=> "string"
 *     "string\n\r".chop   #=> "string\n"
 *     "string\n".chop     #=> "string"
 *     "string".chop       #=> "strin"
 *     "x".chop.chop       #=> ""
 */

static VALUE
rb_str_chop(VALUE str)
{
    return rb_str_subseq(str, 0, chopped_length(str));
}


/*
 *  call-seq:
 *     str.chomp!(separator=$/)   -> str or nil
 *
 *  Modifies <i>str</i> in place as described for <code>String#chomp</code>,
 *  returning <i>str</i>, or <code>nil</code> if no modifications were made.
 */

static VALUE
rb_str_chomp_bang(int argc, VALUE *argv, VALUE str)
{
    rb_encoding *enc;
    VALUE rs;
    int newline;
    char *p, *pp, *e;
    long len, rslen;

    str_modify_keep_cr(str);
    len = RSTRING_LEN(str);
    if (len == 0) return Qnil;
    p = RSTRING_PTR(str);
    e = p + len;
    if (argc == 0) {
        rs = rb_rs;
        if (rs == rb_default_rs) {
          smart_chomp:
            enc = rb_enc_get(str);
            if (rb_enc_mbminlen(enc) > 1) {
                pp = rb_enc_left_char_head(p, e-rb_enc_mbminlen(enc), e, enc);
                if (rb_enc_is_newline(pp, e, enc)) {
                    e = pp;
                }
                pp = e - rb_enc_mbminlen(enc);
                if (pp >= p) {
                    pp = rb_enc_left_char_head(p, pp, e, enc);
                    if (rb_enc_ascget(pp, e, 0, enc) == '\r') {
                        e = pp;
                    }
                }
                if (e == RSTRING_END(str)) {
                    return Qnil;
                }
                len = e - RSTRING_PTR(str);
                STR_SET_LEN(str, len);
            }
            else {
                if (RSTRING_PTR(str)[len-1] == '\n') {
                    STR_DEC_LEN(str);
                    if (RSTRING_LEN(str) > 0 &&
                        RSTRING_PTR(str)[RSTRING_LEN(str)-1] == '\r') {
                        STR_DEC_LEN(str);
                    }
                }
                else if (RSTRING_PTR(str)[len-1] == '\r') {
                    STR_DEC_LEN(str);
                }
                else {
                    return Qnil;
                }
            }
            RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';
            return str;
        }
    }
    else {
        rb_scan_args(argc, argv, "01", &rs);
    }
    if (NIL_P(rs)) return Qnil;
    StringValue(rs);
    rslen = RSTRING_LEN(rs);
    if (rslen == 0) {
        while (len>0 && p[len-1] == '\n') {
            len--;
            if (len>0 && p[len-1] == '\r')
                len--;
        }
        if (len < RSTRING_LEN(str)) {
            STR_SET_LEN(str, len);
            RSTRING_PTR(str)[len] = '\0';
            return str;
        }
        return Qnil;
    }
    if (rslen > len) return Qnil;
    newline = RSTRING_PTR(rs)[rslen-1];
    if (rslen == 1 && newline == '\n')
        goto smart_chomp;

    enc = rb_enc_check(str, rs);
    if (is_broken_string(rs)) {
        return Qnil;
    }
    pp = e - rslen;
    if (p[len-1] == newline &&
        (rslen <= 1 ||
         memcmp(RSTRING_PTR(rs), pp, rslen) == 0)) {
        if (rb_enc_left_char_head(p, pp, e, enc) != pp)
            return Qnil;
        if (ENC_CODERANGE(str) != ENC_CODERANGE_7BIT) {
            ENC_CODERANGE_CLEAR(str);
        }
        STR_SET_LEN(str, RSTRING_LEN(str) - rslen);
        RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';
        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.chomp(separator=$/)   -> new_str
 *
 *  Returns a new <code>String</code> with the given record separator removed
 *  from the end of <i>str</i> (if present). If <code>$/</code> has not been
 *  changed from the default Ruby record separator, then <code>chomp</code> also
 *  removes carriage return characters (that is it will remove <code>\n</code>,
 *  <code>\r</code>, and <code>\r\n</code>). If <code>$/</code> is an empty string,
 *  it will remove all trailing newlines from the string.
 *
 *     "hello".chomp                #=> "hello"
 *     "hello\n".chomp              #=> "hello"
 *     "hello\r\n".chomp            #=> "hello"
 *     "hello\n\r".chomp            #=> "hello\n"
 *     "hello\r".chomp              #=> "hello"
 *     "hello \n there".chomp       #=> "hello \n there"
 *     "hello".chomp("llo")         #=> "he"
 *     "hello\r\n\r\n".chomp('')    #=> "hello"
 *     "hello\r\n\r\r\n".chomp('')  #=> "hello\r\n\r"
 */

static VALUE
rb_str_chomp(int argc, VALUE *argv, VALUE str)
{
    str = rb_str_dup(str);
    rb_str_chomp_bang(argc, argv, str);
    return str;
}

/*
 *  call-seq:
 *     str.lstrip!   -> self or nil
 *
 *  Removes leading whitespace from <i>str</i>, returning <code>nil</code> if no
 *  change was made. See also <code>String#rstrip!</code> and
 *  <code>String#strip!</code>.
 *
 *     "  hello  ".lstrip   #=> "hello  "
 *     "hello".lstrip!      #=> nil
 */

static VALUE
rb_str_lstrip_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *t, *e;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    s = RSTRING_PTR(str);
    if (!s || RSTRING_LEN(str) == 0) return Qnil;
    e = t = RSTRING_END(str);
    /* remove spaces at head */
    while (s < e) {
        int n;
        unsigned int cc = rb_enc_codepoint_len(s, e, &n, enc);

        if (!rb_isspace(cc)) break;
        s += n;
    }

    if (s > RSTRING_PTR(str)) {
        STR_SET_LEN(str, t-s);
        memmove(RSTRING_PTR(str), s, RSTRING_LEN(str));
        RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';
        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.lstrip   -> new_str
 *
 *  Returns a copy of <i>str</i> with leading whitespace removed. See also
 *  <code>String#rstrip</code> and <code>String#strip</code>.
 *
 *     "  hello  ".lstrip   #=> "hello  "
 *     "hello".lstrip       #=> "hello"
 */

static VALUE
rb_str_lstrip(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_lstrip_bang(str);
    return str;
}


/*
 *  call-seq:
 *     str.rstrip!   -> self or nil
 *
 *  Removes trailing whitespace from <i>str</i>, returning <code>nil</code> if
 *  no change was made. See also <code>String#lstrip!</code> and
 *  <code>String#strip!</code>.
 *
 *     "  hello  ".rstrip   #=> "  hello"
 *     "hello".rstrip!      #=> nil
 */

static VALUE
rb_str_rstrip_bang(VALUE str)
{
    rb_encoding *enc;
    char *s, *t, *e;

    str_modify_keep_cr(str);
    enc = STR_ENC_GET(str);
    rb_str_check_dummy_enc(enc);
    s = RSTRING_PTR(str);
    if (!s || RSTRING_LEN(str) == 0) return Qnil;
    t = e = RSTRING_END(str);

    /* remove trailing spaces or '\0's */
    if (single_byte_optimizable(str)) {
        unsigned char c;
        while (s < t && ((c = *(t-1)) == '\0' || ascii_isspace(c))) t--;
    }
    else {
        char *tp;

        while ((tp = rb_enc_prev_char(s, t, e, enc)) != NULL) {
            unsigned int c = rb_enc_codepoint(tp, e, enc);
            if (c && !rb_isspace(c)) break;
            t = tp;
        }
    }
    if (t < e) {
        long len = t-RSTRING_PTR(str);

        STR_SET_LEN(str, len);
        RSTRING_PTR(str)[len] = '\0';
        return str;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.rstrip   -> new_str
 *
 *  Returns a copy of <i>str</i> with trailing whitespace removed. See also
 *  <code>String#lstrip</code> and <code>String#strip</code>.
 *
 *     "  hello  ".rstrip   #=> "  hello"
 *     "hello".rstrip       #=> "hello"
 */

static VALUE
rb_str_rstrip(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_rstrip_bang(str);
    return str;
}


/*
 *  call-seq:
 *     str.strip!   -> str or nil
 *
 *  Removes leading and trailing whitespace from <i>str</i>. Returns
 *  <code>nil</code> if <i>str</i> was not altered.
 */

static VALUE
rb_str_strip_bang(VALUE str)
{
    VALUE l = rb_str_lstrip_bang(str);
    VALUE r = rb_str_rstrip_bang(str);

    if (NIL_P(l) && NIL_P(r)) return Qnil;
    return str;
}


/*
 *  call-seq:
 *     str.strip   -> new_str
 *
 *  Returns a copy of <i>str</i> with leading and trailing whitespace removed.
 *
 *     "    hello    ".strip   #=> "hello"
 *     "\tgoodbye\r\n".strip   #=> "goodbye"
 */

static VALUE
rb_str_strip(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_strip_bang(str);
    return str;
}

static VALUE
scan_once(VALUE str, VALUE pat, long *start)
{
    VALUE result, match;
    struct re_registers *regs;
    int i;

    if (rb_reg_search(pat, str, *start, 0) >= 0) {
        match = rb_backref_get();
        regs = RMATCH_REGS(match);
        if (BEG(0) == END(0)) {
            rb_encoding *enc = STR_ENC_GET(str);
            /*
             * Always consume at least one character of the input string
             */
            if (RSTRING_LEN(str) > END(0))
                *start = END(0)+rb_enc_fast_mbclen(RSTRING_PTR(str)+END(0),
                                                   RSTRING_END(str), enc);
            else
                *start = END(0)+1;
        }
        else {
            *start = END(0);
        }
        if (regs->num_regs == 1) {
            return rb_reg_nth_match(0, match);
        }
        result = rb_ary_new2(regs->num_regs);
        for (i=1; i < regs->num_regs; i++) {
            rb_ary_push(result, rb_reg_nth_match(i, match));
        }

        return result;
    }
    return Qnil;
}


/*
 *  call-seq:
 *     str.scan(pattern)                         -> array
 *     str.scan(pattern) {|match, ...| block }   -> str
 *
 *  Both forms iterate through <i>str</i>, matching the pattern (which may be a
 *  <code>Regexp</code> or a <code>String</code>). For each match, a result is
 *  generated and either added to the result array or passed to the block. If
 *  the pattern contains no groups, each individual result consists of the
 *  matched string, <code>$&</code>.  If the pattern contains groups, each
 *  individual result is itself an array containing one entry per group.
 *
 *     a = "cruel world"
 *     a.scan(/\w+/)        #=> ["cruel", "world"]
 *     a.scan(/.../)        #=> ["cru", "el ", "wor"]
 *     a.scan(/(...)/)      #=> [["cru"], ["el "], ["wor"]]
 *     a.scan(/(..)(..)/)   #=> [["cr", "ue"], ["l ", "wo"]]
 *
 *  And the block form:
 *
 *     a.scan(/\w+/) {|w| print "<<#{w}>> " }
 *     print "\n"
 *     a.scan(/(.)(.)/) {|x,y| print y, x }
 *     print "\n"
 *
 *  <em>produces:</em>
 *
 *     <<cruel>> <<world>>
 *     rceu lowlr
 */

static VALUE
rb_str_scan(VALUE str, VALUE pat)
{
    VALUE result;
    long start = 0;
    long last = -1, prev = 0;
    char *p = RSTRING_PTR(str); long len = RSTRING_LEN(str);

    pat = get_pat(pat, 1);
    if (!rb_block_given_p()) {
        VALUE ary = rb_ary_new();

        while (!NIL_P(result = scan_once(str, pat, &start))) {
            last = prev;
            prev = start;
            rb_ary_push(ary, result);
        }
        if (last >= 0) rb_reg_search(pat, str, last, 0);
        return ary;
    }

    while (!NIL_P(result = scan_once(str, pat, &start))) {
        last = prev;
        prev = start;
        rb_yield(result);
        str_mod_check(str, p, len);
    }
    if (last >= 0) rb_reg_search(pat, str, last, 0);
    return str;
}


/*
 *  call-seq:
 *     str.hex   -> integer
 *
 *  Treats leading characters from <i>str</i> as a string of hexadecimal digits
 *  (with an optional sign and an optional <code>0x</code>) and returns the
 *  corresponding number. Zero is returned on error.
 *
 *     "0x0a".hex     #=> 10
 *     "-1234".hex    #=> -4660
 *     "0".hex        #=> 0
 *     "wombat".hex   #=> 0
 */

static VALUE
rb_str_hex(VALUE str)
{
    return rb_str_to_inum(str, 16, FALSE);
}


/*
 *  call-seq:
 *     str.oct   -> integer
 *
 *  Treats leading characters of <i>str</i> as a string of octal digits (with an
 *  optional sign) and returns the corresponding number.  Returns 0 if the
 *  conversion fails.
 *
 *     "123".oct       #=> 83
 *     "-377".oct      #=> -255
 *     "bad".oct       #=> 0
 *     "0377bad".oct   #=> 255
 */

static VALUE
rb_str_oct(VALUE str)
{
    return rb_str_to_inum(str, -8, FALSE);
}


/*
 *  call-seq:
 *     str.crypt(salt_str)   -> new_str
 *
 *  Applies a one-way cryptographic hash to <i>str</i> by invoking the
 *  standard library function <code>crypt(3)</code> with the given
 *  salt string.  While the format and the result are system and
 *  implementation dependent, using a salt matching the regular
 *  expression <code>\A[a-zA-Z0-9./]{2}</code> should be valid and
 *  safe on any platform, in which only the first two characters are
 *  significant.
 *
 *  This method is for use in system specific scripts, so if you want
 *  a cross-platform hash function consider using Digest or OpenSSL
 *  instead.
 */

static VALUE
rb_str_crypt(VALUE str, VALUE salt)
{
    extern char *crypt(const char *, const char *);
    VALUE result;
    const char *s, *saltp;
    char *res;
#ifdef BROKEN_CRYPT
    char salt_8bit_clean[3];
#endif

    StringValue(salt);
    if (RSTRING_LEN(salt) < 2)
        rb_raise(rb_eArgError, "salt too short (need >=2 bytes)");

    s = RSTRING_PTR(str);
    if (!s) s = "";
    saltp = RSTRING_PTR(salt);
#ifdef BROKEN_CRYPT
    if (!ISASCII((unsigned char)saltp[0]) || !ISASCII((unsigned char)saltp[1])) {
        salt_8bit_clean[0] = saltp[0] & 0x7f;
        salt_8bit_clean[1] = saltp[1] & 0x7f;
        salt_8bit_clean[2] = '\0';
        saltp = salt_8bit_clean;
    }
#endif
    res = crypt(s, saltp);
    if (!res) {
        rb_sys_fail("crypt");
    }
    result = rb_str_new2(res);
    FL_SET_RAW(result, OBJ_TAINTED_RAW(str) | OBJ_TAINTED_RAW(salt));
    return result;
}


/*
 *  call-seq:
 *     str.intern   -> symbol
 *     str.to_sym   -> symbol
 *
 *  Returns the <code>Symbol</code> corresponding to <i>str</i>, creating the
 *  symbol if it did not previously exist. See <code>Symbol#id2name</code>.
 *
 *     "Koala".intern         #=> :Koala
 *     s = 'cat'.to_sym       #=> :cat
 *     s == :cat              #=> true
 *     s = '@cat'.to_sym      #=> :@cat
 *     s == :@cat             #=> true
 *
 *  This can also be used to create symbols that cannot be represented using the
 *  <code>:xxx</code> notation.
 *
 *     'cat and dog'.to_sym   #=> :"cat and dog"
 */

VALUE
rb_str_intern(VALUE s)
{
    VALUE str = RB_GC_GUARD(s);
    ID id;

    id = rb_intern_str(str);
    return ID2SYM(id);
}


/*
 *  call-seq:
 *     str.ord   -> integer
 *
 *  Return the <code>Integer</code> ordinal of a one-character string.
 *
 *     "a".ord         #=> 97
 */

VALUE
rb_str_ord(VALUE s)
{
    unsigned int c;

    c = rb_enc_codepoint(RSTRING_PTR(s), RSTRING_END(s), STR_ENC_GET(s));
    return UINT2NUM(c);
}
/*
 *  call-seq:
 *     str.sum(n=16)   -> integer
 *
 *  Returns a basic <em>n</em>-bit checksum of the characters in <i>str</i>,
 *  where <em>n</em> is the optional <code>Fixnum</code> parameter, defaulting
 *  to 16. The result is simply the sum of the binary value of each character in
 *  <i>str</i> modulo <code>2**n - 1</code>. This is not a particularly good
 *  checksum.
 */

static VALUE
rb_str_sum(int argc, VALUE *argv, VALUE str)
{
    VALUE vbits;
    int bits;
    char *ptr, *p, *pend;
    long len;
    VALUE sum = INT2FIX(0);
    unsigned long sum0 = 0;

    if (argc == 0) {
        bits = 16;
    }
    else {
        rb_scan_args(argc, argv, "01", &vbits);
        bits = NUM2INT(vbits);
    }
    ptr = p = RSTRING_PTR(str);
    len = RSTRING_LEN(str);
    pend = p + len;

    while (p < pend) {
        if (FIXNUM_MAX - UCHAR_MAX < sum0) {
            sum = rb_funcall(sum, '+', 1, LONG2FIX(sum0));
            str_mod_check(str, ptr, len);
            sum0 = 0;
        }
        sum0 += (unsigned char)*p;
        p++;
    }

    if (bits == 0) {
        if (sum0) {
            sum = rb_funcall(sum, '+', 1, LONG2FIX(sum0));
        }
    }
    else {
        if (sum == INT2FIX(0)) {
            if (bits < (int)sizeof(long)*CHAR_BIT) {
                sum0 &= (((unsigned long)1)<<bits)-1;
            }
            sum = LONG2FIX(sum0);
        }
        else {
            VALUE mod;

            if (sum0) {
                sum = rb_funcall(sum, '+', 1, LONG2FIX(sum0));
            }

            mod = rb_funcall(INT2FIX(1), rb_intern("<<"), 1, INT2FIX(bits));
            mod = rb_funcall(mod, '-', 1, INT2FIX(1));
            sum = rb_funcall(sum, '&', 1, mod);
        }
    }
    return sum;
}

static VALUE
rb_str_justify(int argc, VALUE *argv, VALUE str, char jflag)
{
    rb_encoding *enc;
    VALUE w;
    long width, len, flen = 1, fclen = 1;
    VALUE res;
    char *p;
    const char *f = " ";
    long n, size, llen, rlen, llen2 = 0, rlen2 = 0;
    volatile VALUE pad;
    int singlebyte = 1, cr;

    rb_scan_args(argc, argv, "11", &w, &pad);
    enc = STR_ENC_GET(str);
    width = NUM2LONG(w);
    if (argc == 2) {
        StringValue(pad);
        enc = rb_enc_check(str, pad);
        f = RSTRING_PTR(pad);
        flen = RSTRING_LEN(pad);
        fclen = str_strlen(pad, enc);
        singlebyte = single_byte_optimizable(pad);
        if (flen == 0 || fclen == 0) {
            rb_raise(rb_eArgError, "zero width padding");
        }
    }
    len = str_strlen(str, enc);
    if (width < 0 || len >= width) return rb_str_dup(str);
    n = width - len;
    llen = (jflag == 'l') ? 0 : ((jflag == 'r') ? n : n/2);
    rlen = n - llen;
    cr = ENC_CODERANGE(str);
    if (flen > 1) {
       llen2 = str_offset(f, f + flen, llen % fclen, enc, singlebyte);
       rlen2 = str_offset(f, f + flen, rlen % fclen, enc, singlebyte);
    }
    size = RSTRING_LEN(str);
    if ((len = llen / fclen + rlen / fclen) >= LONG_MAX / flen ||
       (len *= flen) >= LONG_MAX - llen2 - rlen2 ||
       (len += llen2 + rlen2) >= LONG_MAX - size) {
       rb_raise(rb_eArgError, "argument too big");
    }
    len += size;
    res = rb_str_new5(str, 0, len);
    p = RSTRING_PTR(res);
    if (flen <= 1) {
       memset(p, *f, llen);
       p += llen;
    }
    else {
       while (llen >= fclen) {
            memcpy(p,f,flen);
            p += flen;
            llen -= fclen;
        }
       if (llen > 0) {
           memcpy(p, f, llen2);
           p += llen2;
        }
    }
    memcpy(p, RSTRING_PTR(str), size);
    p += size;
    if (flen <= 1) {
       memset(p, *f, rlen);
       p += rlen;
    }
    else {
       while (rlen >= fclen) {
            memcpy(p,f,flen);
            p += flen;
            rlen -= fclen;
        }
       if (rlen > 0) {
           memcpy(p, f, rlen2);
           p += rlen2;
        }
    }
    *p = '\0';
    STR_SET_LEN(res, p-RSTRING_PTR(res));
    OBJ_INFECT_RAW(res, str);
    if (!NIL_P(pad)) OBJ_INFECT_RAW(res, pad);
    rb_enc_associate(res, enc);
    if (argc == 2)
        cr = ENC_CODERANGE_AND(cr, ENC_CODERANGE(pad));
    if (cr != ENC_CODERANGE_BROKEN)
        ENC_CODERANGE_SET(res, cr);
    return res;
}


/*
 *  call-seq:
 *     str.ljust(integer, padstr=' ')   -> new_str
 *
 *  If <i>integer</i> is greater than the length of <i>str</i>, returns a new
 *  <code>String</code> of length <i>integer</i> with <i>str</i> left justified
 *  and padded with <i>padstr</i>; otherwise, returns <i>str</i>.
 *
 *     "hello".ljust(4)            #=> "hello"
 *     "hello".ljust(20)           #=> "hello               "
 *     "hello".ljust(20, '1234')   #=> "hello123412341234123"
 */

static VALUE
rb_str_ljust(int argc, VALUE *argv, VALUE str)
{
    return rb_str_justify(argc, argv, str, 'l');
}


/*
 *  call-seq:
 *     str.rjust(integer, padstr=' ')   -> new_str
 *
 *  If <i>integer</i> is greater than the length of <i>str</i>, returns a new
 *  <code>String</code> of length <i>integer</i> with <i>str</i> right justified
 *  and padded with <i>padstr</i>; otherwise, returns <i>str</i>.
 *
 *     "hello".rjust(4)            #=> "hello"
 *     "hello".rjust(20)           #=> "               hello"
 *     "hello".rjust(20, '1234')   #=> "123412341234123hello"
 */

static VALUE
rb_str_rjust(int argc, VALUE *argv, VALUE str)
{
    return rb_str_justify(argc, argv, str, 'r');
}


/*
 *  call-seq:
 *     str.center(width, padstr=' ')   -> new_str
 *
 *  Centers +str+ in +width+.  If +width+ is greater than the length of +str+,
 *  returns a new String of length +width+ with +str+ centered and padded with
 *  +padstr+; otherwise, returns +str+.
 *
 *     "hello".center(4)         #=> "hello"
 *     "hello".center(20)        #=> "       hello        "
 *     "hello".center(20, '123') #=> "1231231hello12312312"
 */

static VALUE
rb_str_center(int argc, VALUE *argv, VALUE str)
{
    return rb_str_justify(argc, argv, str, 'c');
}

/*
 *  call-seq:
 *     str.partition(sep)              -> [head, sep, tail]
 *     str.partition(regexp)           -> [head, match, tail]
 *
 *  Searches <i>sep</i> or pattern (<i>regexp</i>) in the string
 *  and returns the part before it, the match, and the part
 *  after it.
 *  If it is not found, returns two empty strings and <i>str</i>.
 *
 *     "hello".partition("l")         #=> ["he", "l", "lo"]
 *     "hello".partition("x")         #=> ["hello", "", ""]
 *     "hello".partition(/.l/)        #=> ["h", "el", "lo"]
 */

static VALUE
rb_str_partition(VALUE str, VALUE sep)
{
    long pos;
    int regex = FALSE;

    if (RB_TYPE_P(sep, T_REGEXP)) {
        pos = rb_reg_search(sep, str, 0, 0);
        regex = TRUE;
    }
    else {
        VALUE tmp;

        tmp = rb_check_string_type(sep);
        if (NIL_P(tmp)) {
            rb_raise(rb_eTypeError, "type mismatch: %s given",
                     rb_obj_classname(sep));
        }
        sep = tmp;
        pos = rb_str_index(str, sep, 0);
    }
    if (pos < 0) {
      failed:
        return rb_ary_new3(3, str, str_new_empty(str), str_new_empty(str));
    }
    if (regex) {
        sep = rb_str_subpat(str, sep, INT2FIX(0));
        if (pos == 0 && RSTRING_LEN(sep) == 0) goto failed;
    }
    return rb_ary_new3(3, rb_str_subseq(str, 0, pos),
                          sep,
                          rb_str_subseq(str, pos+RSTRING_LEN(sep),
                                             RSTRING_LEN(str)-pos-RSTRING_LEN(sep)));
}

/*
 *  call-seq:
 *     str.rpartition(sep)             -> [head, sep, tail]
 *     str.rpartition(regexp)          -> [head, match, tail]
 *
 *  Searches <i>sep</i> or pattern (<i>regexp</i>) in the string from the end
 *  of the string, and returns the part before it, the match, and the part
 *  after it.
 *  If it is not found, returns two empty strings and <i>str</i>.
 *
 *     "hello".rpartition("l")         #=> ["hel", "l", "o"]
 *     "hello".rpartition("x")         #=> ["", "", "hello"]
 *     "hello".rpartition(/.l/)        #=> ["he", "ll", "o"]
 */

static VALUE
rb_str_rpartition(VALUE str, VALUE sep)
{
    long pos = RSTRING_LEN(str);
    int regex = FALSE;

    if (RB_TYPE_P(sep, T_REGEXP)) {
        pos = rb_reg_search(sep, str, pos, 1);
        regex = TRUE;
    }
    else {
        VALUE tmp;

        tmp = rb_check_string_type(sep);
        if (NIL_P(tmp)) {
            rb_raise(rb_eTypeError, "type mismatch: %s given",
                     rb_obj_classname(sep));
        }
        sep = tmp;
        pos = rb_str_sublen(str, pos);
        pos = rb_str_rindex(str, sep, pos);
    }
    if (pos < 0) {
        return rb_ary_new3(3, str_new_empty(str), str_new_empty(str), str);
    }
    if (regex) {
        sep = rb_reg_nth_match(0, rb_backref_get());
    }
    else {
        pos = rb_str_offset(str, pos);
    }
    return rb_ary_new3(3, rb_str_subseq(str, 0, pos),
                          sep,
                          rb_str_subseq(str, pos+RSTRING_LEN(sep),
                                        RSTRING_LEN(str)-pos-RSTRING_LEN(sep)));
}

/*
 *  call-seq:
 *     str.start_with?([prefixes]+)   -> true or false
 *
 *  Returns true if +str+ starts with one of the +prefixes+ given.
 *
 *    "hello".start_with?("hell")               #=> true
 *
 *    # returns true if one of the prefixes matches.
 *    "hello".start_with?("heaven", "hell")     #=> true
 *    "hello".start_with?("heaven", "paradise") #=> false
 */

static VALUE
rb_str_start_with(int argc, VALUE *argv, VALUE str)
{
    int i;

    for (i=0; i<argc; i++) {
        VALUE tmp = argv[i];
        StringValue(tmp);
        rb_enc_check(str, tmp);
        if (RSTRING_LEN(str) < RSTRING_LEN(tmp)) continue;
        if (memcmp(RSTRING_PTR(str), RSTRING_PTR(tmp), RSTRING_LEN(tmp)) == 0)
            return Qtrue;
    }
    return Qfalse;
}

/*
 *  call-seq:
 *     str.end_with?([suffixes]+)   -> true or false
 *
 *  Returns true if +str+ ends with one of the +suffixes+ given.
 */

static VALUE
rb_str_end_with(int argc, VALUE *argv, VALUE str)
{
    int i;
    char *p, *s, *e;
    rb_encoding *enc;

    for (i=0; i<argc; i++) {
        VALUE tmp = argv[i];
        StringValue(tmp);
        enc = rb_enc_check(str, tmp);
        if (RSTRING_LEN(str) < RSTRING_LEN(tmp)) continue;
        p = RSTRING_PTR(str);
        e = p + RSTRING_LEN(str);
        s = e - RSTRING_LEN(tmp);
        if (rb_enc_left_char_head(p, s, e, enc) != s)
            continue;
        if (memcmp(s, RSTRING_PTR(tmp), RSTRING_LEN(tmp)) == 0)
            return Qtrue;
    }
    return Qfalse;
}

void
rb_str_setter(VALUE val, ID id, VALUE *var)
{
    if (!NIL_P(val) && !RB_TYPE_P(val, T_STRING)) {
        rb_raise(rb_eTypeError, "value of %s must be String", rb_id2name(id));
    }
    *var = val;
}


/*
 *  call-seq:
 *     str.force_encoding(encoding)   -> str
 *
 *  Changes the encoding to +encoding+ and returns self.
 */

static VALUE
rb_str_force_encoding(VALUE str, VALUE enc)
{
    str_modifiable(str);
    rb_enc_associate(str, rb_to_encoding(enc));
    ENC_CODERANGE_CLEAR(str);
    return str;
}

/*
 *  call-seq:
 *     str.b   -> str
 *
 *  Returns a copied string whose encoding is ASCII-8BIT.
 */

static VALUE
rb_str_b(VALUE str)
{
    VALUE str2 = str_alloc(rb_cString);
    str_replace_shared_without_enc(str2, str);
    OBJ_INFECT_RAW(str2, str);
    ENC_CODERANGE_CLEAR(str2);
    return str2;
}

/*
 *  call-seq:
 *     str.valid_encoding?  -> true or false
 *
 *  Returns true for a string which encoded correctly.
 *
 *    "\xc2\xa1".force_encoding("UTF-8").valid_encoding?  #=> true
 *    "\xc2".force_encoding("UTF-8").valid_encoding?      #=> false
 *    "\x80".force_encoding("UTF-8").valid_encoding?      #=> false
 */

static VALUE
rb_str_valid_encoding_p(VALUE str)
{
    int cr = rb_enc_str_coderange(str);

    return cr == ENC_CODERANGE_BROKEN ? Qfalse : Qtrue;
}

/*
 *  call-seq:
 *     str.ascii_only?  -> true or false
 *
 *  Returns true for a string which has only ASCII characters.
 *
 *    "abc".force_encoding("UTF-8").ascii_only?          #=> true
 *    "abc\u{6666}".force_encoding("UTF-8").ascii_only?  #=> false
 */

static VALUE
rb_str_is_ascii_only_p(VALUE str)
{
    int cr = rb_enc_str_coderange(str);

    return cr == ENC_CODERANGE_7BIT ? Qtrue : Qfalse;
}

VALUE
rb_str_ellipsize(VALUE str, long len)
{
    static const char ellipsis[] = "...";
    const long ellipsislen = sizeof(ellipsis) - 1;
    rb_encoding *const enc = rb_enc_get(str);
    const long blen = RSTRING_LEN(str);
    const char *const p = RSTRING_PTR(str), *e = p + blen;
    VALUE estr, ret = 0;

    if (len < 0) rb_raise(rb_eIndexError, "negative length %ld", len);
    if (len * rb_enc_mbminlen(enc) >= blen ||
        (e = rb_enc_nth(p, e, len, enc)) - p == blen) {
        ret = str;
    }
    else if (len <= ellipsislen ||
             !(e = rb_enc_step_back(p, e, e, len = ellipsislen, enc))) {
        if (rb_enc_asciicompat(enc)) {
            ret = rb_str_new_with_class(str, ellipsis, len);
            rb_enc_associate(ret, enc);
        }
        else {
            estr = rb_usascii_str_new(ellipsis, len);
            ret = rb_str_encode(estr, rb_enc_from_encoding(enc), 0, Qnil);
        }
    }
    else if (ret = rb_str_subseq(str, 0, e - p), rb_enc_asciicompat(enc)) {
        rb_str_cat(ret, ellipsis, ellipsislen);
    }
    else {
        estr = rb_str_encode(rb_usascii_str_new(ellipsis, ellipsislen),
                             rb_enc_from_encoding(enc), 0, Qnil);
        rb_str_append(ret, estr);
    }
    return ret;
}

static VALUE
str_compat_and_valid(VALUE str, rb_encoding *enc)
{
    int cr;
    str = StringValue(str);
    cr = rb_enc_str_coderange(str);
    if (cr == ENC_CODERANGE_BROKEN) {
        rb_raise(rb_eArgError, "replacement must be valid byte sequence '%+"PRIsVALUE"'", str);
    }
    else if (cr == ENC_CODERANGE_7BIT) {
        rb_encoding *e = STR_ENC_GET(str);
        if (!rb_enc_asciicompat(enc)) {
            rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
                    rb_enc_name(enc), rb_enc_name(e));
        }
    }
    else { /* ENC_CODERANGE_VALID */
        rb_encoding *e = STR_ENC_GET(str);
        if (enc != e) {
            rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
                    rb_enc_name(enc), rb_enc_name(e));
        }
    }
    return str;
}

VALUE
rb_str_scrub(VALUE str, VALUE repl)
{
    int cr = ENC_CODERANGE(str);
    rb_encoding *enc;
    int encidx;
    VALUE buf = Qnil;
    const char *rep;
    long replen;
    int tainted = 0;

    if (cr == ENC_CODERANGE_7BIT || cr == ENC_CODERANGE_VALID)
        return Qnil;

    enc = STR_ENC_GET(str);
    if (!NIL_P(repl)) {
        repl = str_compat_and_valid(repl, enc);
        tainted = OBJ_TAINTED_RAW(repl);
    }

    if (rb_enc_dummy_p(enc)) {
        return Qnil;
    }
    encidx = rb_enc_to_index(enc);

#define DEFAULT_REPLACE_CHAR(str) do { \
        static const char replace[sizeof(str)-1] = str; \
        rep = replace; replen = (int)sizeof(replace); \
    } while (0)

    if (rb_enc_asciicompat(enc)) {
        const char *p = RSTRING_PTR(str);
        const char *e = RSTRING_END(str);
        const char *p1 = p;
        int rep7bit_p;
        if (rb_block_given_p()) {
            rep = NULL;
            replen = 0;
            rep7bit_p = FALSE;
        }
        else if (!NIL_P(repl)) {
            rep = RSTRING_PTR(repl);
            replen = RSTRING_LEN(repl);
            rep7bit_p = (ENC_CODERANGE(repl) == ENC_CODERANGE_7BIT);
        }
        else if (encidx == rb_utf8_encindex()) {
            DEFAULT_REPLACE_CHAR("\xEF\xBF\xBD");
            rep7bit_p = FALSE;
        }
        else {
            DEFAULT_REPLACE_CHAR("?");
            rep7bit_p = TRUE;
        }
        cr = ENC_CODERANGE_7BIT;

        p = search_nonascii(p, e);
        if (!p) {
            p = e;
        }
        while (p < e) {
            int ret = rb_enc_precise_mbclen(p, e, enc);
            if (MBCLEN_NEEDMORE_P(ret)) {
                break;
            }
            else if (MBCLEN_CHARFOUND_P(ret)) {
                cr = ENC_CODERANGE_VALID;
                p += MBCLEN_CHARFOUND_LEN(ret);
            }
            else if (MBCLEN_INVALID_P(ret)) {
                /*
                 * p1~p: valid ascii/multibyte chars
                 * p ~e: invalid bytes + unknown bytes
                 */
                long clen = rb_enc_mbmaxlen(enc);
                if (NIL_P(buf)) buf = rb_str_buf_new(RSTRING_LEN(str));
                if (p > p1) {
                    rb_str_buf_cat(buf, p1, p - p1);
                }

                if (e - p < clen) clen = e - p;
                if (clen <= 2) {
                    clen = 1;
                }
                else {
                    const char *q = p;
                    clen--;
                    for (; clen > 1; clen--) {
                        ret = rb_enc_precise_mbclen(q, q + clen, enc);
                        if (MBCLEN_NEEDMORE_P(ret)) break;
                        if (MBCLEN_INVALID_P(ret)) continue;
                        UNREACHABLE;
                    }
                }
                if (rep) {
                    rb_str_buf_cat(buf, rep, replen);
                    if (!rep7bit_p) cr = ENC_CODERANGE_VALID;
                }
                else {
                    repl = rb_yield(rb_enc_str_new(p, clen, enc));
                    repl = str_compat_and_valid(repl, enc);
                    tainted |= OBJ_TAINTED_RAW(repl);
                    rb_str_buf_cat(buf, RSTRING_PTR(repl), RSTRING_LEN(repl));
                    if (ENC_CODERANGE(repl) == ENC_CODERANGE_VALID)
                        cr = ENC_CODERANGE_VALID;
                }
                p += clen;
                p1 = p;
                p = search_nonascii(p, e);
                if (!p) {
                    p = e;
                    break;
                }
            }
            else {
                UNREACHABLE;
            }
        }
        if (NIL_P(buf)) {
            if (p == e) {
                ENC_CODERANGE_SET(str, cr);
                return Qnil;
            }
            buf = rb_str_buf_new(RSTRING_LEN(str));
        }
        if (p1 < p) {
            rb_str_buf_cat(buf, p1, p - p1);
        }
        if (p < e) {
            if (rep) {
                rb_str_buf_cat(buf, rep, replen);
                if (!rep7bit_p) cr = ENC_CODERANGE_VALID;
            }
            else {
                repl = rb_yield(rb_enc_str_new(p, e-p, enc));
                repl = str_compat_and_valid(repl, enc);
                tainted |= OBJ_TAINTED_RAW(repl);
                rb_str_buf_cat(buf, RSTRING_PTR(repl), RSTRING_LEN(repl));
                if (ENC_CODERANGE(repl) == ENC_CODERANGE_VALID)
                    cr = ENC_CODERANGE_VALID;
            }
        }
    }
    else {
        /* ASCII incompatible */
        const char *p = RSTRING_PTR(str);
        const char *e = RSTRING_END(str);
        const char *p1 = p;
        long mbminlen = rb_enc_mbminlen(enc);
        if (!NIL_P(repl)) {
            rep = RSTRING_PTR(repl);
            replen = RSTRING_LEN(repl);
        }
        else if (encidx == ENCINDEX_UTF_16BE) {
            DEFAULT_REPLACE_CHAR("\xFF\xFD");
        }
        else if (encidx == ENCINDEX_UTF_16LE) {
            DEFAULT_REPLACE_CHAR("\xFD\xFF");
        }
        else if (encidx == ENCINDEX_UTF_32BE) {
            DEFAULT_REPLACE_CHAR("\x00\x00\xFF\xFD");
        }
        else if (encidx == ENCINDEX_UTF_32LE) {
            DEFAULT_REPLACE_CHAR("\xFD\xFF\x00\x00");
        }
        else {
            DEFAULT_REPLACE_CHAR("?");
        }

        while (p < e) {
            int ret = rb_enc_precise_mbclen(p, e, enc);
            if (MBCLEN_NEEDMORE_P(ret)) {
                break;
            }
            else if (MBCLEN_CHARFOUND_P(ret)) {
                p += MBCLEN_CHARFOUND_LEN(ret);
            }
            else if (MBCLEN_INVALID_P(ret)) {
                const char *q = p;
                long clen = rb_enc_mbmaxlen(enc);
                if (NIL_P(buf)) buf = rb_str_buf_new(RSTRING_LEN(str));
                if (p > p1) rb_str_buf_cat(buf, p1, p - p1);

                if (e - p < clen) clen = e - p;
                if (clen <= mbminlen * 2) {
                    clen = mbminlen;
                }
                else {
                    clen -= mbminlen;
                    for (; clen > mbminlen; clen-=mbminlen) {
                        ret = rb_enc_precise_mbclen(q, q + clen, enc);
                        if (MBCLEN_NEEDMORE_P(ret)) break;
                        if (MBCLEN_INVALID_P(ret)) continue;
                        UNREACHABLE;
                    }
                }
                if (rep) {
                    rb_str_buf_cat(buf, rep, replen);
                }
                else {
                    repl = rb_yield(rb_enc_str_new(p, e-p, enc));
                    repl = str_compat_and_valid(repl, enc);
                    tainted |= OBJ_TAINTED_RAW(repl);
                    rb_str_buf_cat(buf, RSTRING_PTR(repl), RSTRING_LEN(repl));
                }
                p += clen;
                p1 = p;
            }
            else {
                UNREACHABLE;
            }
        }
        if (NIL_P(buf)) {
            if (p == e) {
                ENC_CODERANGE_SET(str, ENC_CODERANGE_VALID);
                return Qnil;
            }
            buf = rb_str_buf_new(RSTRING_LEN(str));
        }
        if (p1 < p) {
            rb_str_buf_cat(buf, p1, p - p1);
        }
        if (p < e) {
            if (rep) {
                rb_str_buf_cat(buf, rep, replen);
            }
            else {
                repl = rb_yield(rb_enc_str_new(p, e-p, enc));
                repl = str_compat_and_valid(repl, enc);
                tainted |= OBJ_TAINTED_RAW(repl);
                rb_str_buf_cat(buf, RSTRING_PTR(repl), RSTRING_LEN(repl));
            }
        }
        cr = ENC_CODERANGE_VALID;
    }
    FL_SET_RAW(buf, tainted|OBJ_TAINTED_RAW(str));
    ENCODING_CODERANGE_SET(buf, rb_enc_to_index(enc), cr);
    return buf;
}

/*
 *  call-seq:
 *    str.scrub -> new_str
 *    str.scrub(repl) -> new_str
 *    str.scrub{|bytes|} -> new_str
 *
 *  If the string is invalid byte sequence then replace invalid bytes with given replacement
 *  character, else returns self.
 *  If block is given, replace invalid bytes with returned value of the block.
 *
 *     "abc\u3042\x81".scrub #=> "abc\u3042\uFFFD"
 *     "abc\u3042\x81".scrub("*") #=> "abc\u3042*"
 *     "abc\u3042\xE3\x80".scrub{|bytes| '<'+bytes.unpack('H*')[0]+'>' } #=> "abc\u3042<e380>"
 */
static VALUE
str_scrub(int argc, VALUE *argv, VALUE str)
{
    VALUE repl = argc ? (rb_check_arity(argc, 0, 1), argv[0]) : Qnil;
    VALUE new = rb_str_scrub(str, repl);
    return NIL_P(new) ? rb_str_dup(str): new;
}

/*
 *  call-seq:
 *    str.scrub! -> str
 *    str.scrub!(repl) -> str
 *    str.scrub!{|bytes|} -> str
 *
 *  If the string is invalid byte sequence then replace invalid bytes with given replacement
 *  character, else returns self.
 *  If block is given, replace invalid bytes with returned value of the block.
 *
 *     "abc\u3042\x81".scrub! #=> "abc\u3042\uFFFD"
 *     "abc\u3042\x81".scrub!("*") #=> "abc\u3042*"
 *     "abc\u3042\xE3\x80".scrub!{|bytes| '<'+bytes.unpack('H*')[0]+'>' } #=> "abc\u3042<e380>"
 */
static VALUE
str_scrub_bang(int argc, VALUE *argv, VALUE str)
{
    VALUE repl = argc ? (rb_check_arity(argc, 0, 1), argv[0]) : Qnil;
    VALUE new = rb_str_scrub(str, repl);
    if (!NIL_P(new)) rb_str_replace(str, new);
    return str;
}

/**********************************************************************
 * Document-class: Symbol
 *
 *  <code>Symbol</code> objects represent names and some strings
 *  inside the Ruby
 *  interpreter. They are generated using the <code>:name</code> and
 *  <code>:"string"</code> literals
 *  syntax, and by the various <code>to_sym</code> methods. The same
 *  <code>Symbol</code> object will be created for a given name or string
 *  for the duration of a program's execution, regardless of the context
 *  or meaning of that name. Thus if <code>Fred</code> is a constant in
 *  one context, a method in another, and a class in a third, the
 *  <code>Symbol</code> <code>:Fred</code> will be the same object in
 *  all three contexts.
 *
 *     module One
 *       class Fred
 *       end
 *       $f1 = :Fred
 *     end
 *     module Two
 *       Fred = 1
 *       $f2 = :Fred
 *     end
 *     def Fred()
 *     end
 *     $f3 = :Fred
 *     $f1.object_id   #=> 2514190
 *     $f2.object_id   #=> 2514190
 *     $f3.object_id   #=> 2514190
 *
 */


/*
 *  call-seq:
 *     sym == obj   -> true or false
 *
 *  Equality---If <i>sym</i> and <i>obj</i> are exactly the same
 *  symbol, returns <code>true</code>.
 */

static VALUE
sym_equal(VALUE sym1, VALUE sym2)
{
    if (sym1 == sym2) return Qtrue;
    return Qfalse;
}


static int
sym_printable(const char *s, const char *send, rb_encoding *enc)
{
    while (s < send) {
        int n;
        int c = rb_enc_codepoint_len(s, send, &n, enc);

        if (!rb_enc_isprint(c, enc)) return FALSE;
        s += n;
    }
    return TRUE;
}

int
rb_str_symname_p(VALUE sym)
{
    rb_encoding *enc;
    const char *ptr;
    long len;
    rb_encoding *resenc = rb_default_internal_encoding();

    if (resenc == NULL) resenc = rb_default_external_encoding();
    enc = STR_ENC_GET(sym);
    ptr = RSTRING_PTR(sym);
    len = RSTRING_LEN(sym);
    if ((resenc != enc && !rb_str_is_ascii_only_p(sym)) || len != (long)strlen(ptr) ||
        !rb_enc_symname_p(ptr, enc) || !sym_printable(ptr, ptr + len, enc)) {
        return FALSE;
    }
    return TRUE;
}

VALUE
rb_str_quote_unprintable(VALUE str)
{
    rb_encoding *enc;
    const char *ptr;
    long len;
    rb_encoding *resenc;

    Check_Type(str, T_STRING);
    resenc = rb_default_internal_encoding();
    if (resenc == NULL) resenc = rb_default_external_encoding();
    enc = STR_ENC_GET(str);
    ptr = RSTRING_PTR(str);
    len = RSTRING_LEN(str);
    if ((resenc != enc && !rb_str_is_ascii_only_p(str)) ||
        !sym_printable(ptr, ptr + len, enc)) {
        return rb_str_inspect(str);
    }
    return str;
}

VALUE
rb_id_quote_unprintable(ID id)
{
    return rb_str_quote_unprintable(rb_id2str(id));
}

/*
 *  call-seq:
 *     sym.inspect    -> string
 *
 *  Returns the representation of <i>sym</i> as a symbol literal.
 *
 *     :fred.inspect   #=> ":fred"
 */

static VALUE
sym_inspect(VALUE sym)
{
    VALUE str;
    const char *ptr;
    long len;
    ID id = SYM2ID(sym);
    char *dest;

    sym = rb_id2str(id);
    if (!rb_str_symname_p(sym)) {
        str = rb_str_inspect(sym);
        len = RSTRING_LEN(str);
        rb_str_resize(str, len + 1);
        dest = RSTRING_PTR(str);
        memmove(dest + 1, dest, len);
        dest[0] = ':';
    }
    else {
        rb_encoding *enc = STR_ENC_GET(sym);
        ptr = RSTRING_PTR(sym);
        len = RSTRING_LEN(sym);
        str = rb_enc_str_new(0, len + 1, enc);
        dest = RSTRING_PTR(str);
        dest[0] = ':';
        memcpy(dest + 1, ptr, len);
    }
    return str;
}


/*
 *  call-seq:
 *     sym.id2name   -> string
 *     sym.to_s      -> string
 *
 *  Returns the name or string corresponding to <i>sym</i>.
 *
 *     :fred.id2name   #=> "fred"
 */


VALUE
rb_sym_to_s(VALUE sym)
{
    ID id = SYM2ID(sym);

    return str_new3(rb_cString, rb_id2str(id));
}


/*
 * call-seq:
 *   sym.to_sym   -> sym
 *   sym.intern   -> sym
 *
 * In general, <code>to_sym</code> returns the <code>Symbol</code> corresponding
 * to an object. As <i>sym</i> is already a symbol, <code>self</code> is returned
 * in this case.
 */

static VALUE
sym_to_sym(VALUE sym)
{
    return sym;
}

static VALUE
sym_call(VALUE args, VALUE sym, int argc, VALUE *argv, VALUE passed_proc)
{
    VALUE obj;

    if (argc < 1) {
        rb_raise(rb_eArgError, "no receiver given");
    }
    obj = argv[0];
    return rb_funcall_with_block(obj, (ID)sym, argc - 1, argv + 1, passed_proc);
}

/*
 * call-seq:
 *   sym.to_proc
 *
 * Returns a _Proc_ object which respond to the given method by _sym_.
 *
 *   (1..3).collect(&:to_s)  #=> ["1", "2", "3"]
 */

static VALUE
sym_to_proc(VALUE sym)
{
    static VALUE sym_proc_cache = Qfalse;
    enum {SYM_PROC_CACHE_SIZE = 67};
    VALUE proc;
    long id, index;
    VALUE *aryp;

    if (!sym_proc_cache) {
        sym_proc_cache = rb_ary_tmp_new(SYM_PROC_CACHE_SIZE * 2);
        rb_gc_register_mark_object(sym_proc_cache);
        rb_ary_store(sym_proc_cache, SYM_PROC_CACHE_SIZE*2 - 1, Qnil);
    }

    id = SYM2ID(sym);
    index = (id % SYM_PROC_CACHE_SIZE) << 1;

    aryp = RARRAY_PTR(sym_proc_cache);
    if (aryp[index] == sym) {
        return aryp[index + 1];
    }
    else {
        proc = rb_proc_new(sym_call, (VALUE)id);
        rb_block_clear_env_self(proc);
        aryp[index] = sym;
        aryp[index + 1] = proc;
        return proc;
    }
}

/*
 * call-seq:
 *
 *   sym.succ
 *
 * Same as <code>sym.to_s.succ.intern</code>.
 */

static VALUE
sym_succ(VALUE sym)
{
    return rb_str_intern(rb_str_succ(rb_sym_to_s(sym)));
}

/*
 * call-seq:
 *
 *   symbol <=> other_symbol       -> -1, 0, +1 or nil
 *
 * Compares +symbol+ with +other_symbol+ after calling #to_s on each of the
 * symbols. Returns -1, 0, +1 or nil depending on whether +symbol+ is less
 * than, equal to, or greater than +other_symbol+.
 *
 *  +nil+ is returned if the two values are incomparable.
 *
 * See String#<=> for more information.
 */

static VALUE
sym_cmp(VALUE sym, VALUE other)
{
    if (!SYMBOL_P(other)) {
        return Qnil;
    }
    return rb_str_cmp_m(rb_sym_to_s(sym), rb_sym_to_s(other));
}

/*
 * call-seq:
 *
 *   sym.casecmp(other)  -> -1, 0, +1 or nil
 *
 * Case-insensitive version of <code>Symbol#<=></code>.
 */

static VALUE
sym_casecmp(VALUE sym, VALUE other)
{
    if (!SYMBOL_P(other)) {
        return Qnil;
    }
    return rb_str_casecmp(rb_sym_to_s(sym), rb_sym_to_s(other));
}

/*
 * call-seq:
 *   sym =~ obj   -> fixnum or nil
 *   sym.match(obj)   -> fixnum or nil
 *
 * Returns <code>sym.to_s =~ obj</code>.
 */

static VALUE
sym_match(VALUE sym, VALUE other)
{
    return rb_str_match(rb_sym_to_s(sym), other);
}

/*
 * call-seq:
 *   sym[idx]      -> char
 *   sym[b, n]     -> string
 *   sym.slice(idx)      -> char
 *   sym.slice(b, n)     -> string
 *
 * Returns <code>sym.to_s[]</code>.
 */

static VALUE
sym_aref(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_aref_m(argc, argv, rb_sym_to_s(sym));
}

/*
 * call-seq:
 *   sym.length    -> integer
 *   sym.size    -> integer
 *
 * Same as <code>sym.to_s.length</code>.
 */

static VALUE
sym_length(VALUE sym)
{
    return rb_str_length(rb_id2str(SYM2ID(sym)));
}

/*
 * call-seq:
 *   sym.empty?   -> true or false
 *
 * Returns that _sym_ is :"" or not.
 */

static VALUE
sym_empty(VALUE sym)
{
    return rb_str_empty(rb_id2str(SYM2ID(sym)));
}

/*
 * call-seq:
 *   sym.upcase    -> symbol
 *
 * Same as <code>sym.to_s.upcase.intern</code>.
 */

static VALUE
sym_upcase(VALUE sym)
{
    return rb_str_intern(rb_str_upcase(rb_id2str(SYM2ID(sym))));
}

/*
 * call-seq:
 *   sym.downcase  -> symbol
 *
 * Same as <code>sym.to_s.downcase.intern</code>.
 */

static VALUE
sym_downcase(VALUE sym)
{
    return rb_str_intern(rb_str_downcase(rb_id2str(SYM2ID(sym))));
}

/*
 * call-seq:
 *   sym.capitalize  -> symbol
 *
 * Same as <code>sym.to_s.capitalize.intern</code>.
 */

static VALUE
sym_capitalize(VALUE sym)
{
    return rb_str_intern(rb_str_capitalize(rb_id2str(SYM2ID(sym))));
}

/*
 * call-seq:
 *   sym.swapcase  -> symbol
 *
 * Same as <code>sym.to_s.swapcase.intern</code>.
 */

static VALUE
sym_swapcase(VALUE sym)
{
    return rb_str_intern(rb_str_swapcase(rb_id2str(SYM2ID(sym))));
}

/*
 * call-seq:
 *   sym.encoding   -> encoding
 *
 * Returns the Encoding object that represents the encoding of _sym_.
 */

static VALUE
sym_encoding(VALUE sym)
{
    return rb_obj_encoding(rb_id2str(SYM2ID(sym)));
}

ID
rb_to_id(VALUE name)
{
    VALUE tmp;

    if (SYMBOL_P(name)) {
        return SYM2ID(name);
    }
    if (!RB_TYPE_P(name, T_STRING)) {
        tmp = rb_check_string_type(name);
        if (NIL_P(tmp)) {
            rb_raise(rb_eTypeError, "%+"PRIsVALUE" is not a symbol",
                     name);
        }
        name = tmp;
    }
    return rb_intern_str(name);
}

/*
 *  A <code>String</code> object holds and manipulates an arbitrary sequence of
 *  bytes, typically representing characters. String objects may be created
 *  using <code>String::new</code> or as literals.
 *
 *  Because of aliasing issues, users of strings should be aware of the methods
 *  that modify the contents of a <code>String</code> object.  Typically,
 *  methods with names ending in ``!'' modify their receiver, while those
 *  without a ``!'' return a new <code>String</code>.  However, there are
 *  exceptions, such as <code>String#[]=</code>.
 *
 */

void
Init_String(void)
{
#undef rb_intern
#define rb_intern(str) rb_intern_const(str)

    rb_cString  = rb_define_class("String", rb_cObject);
    rb_include_module(rb_cString, rb_mComparable);
    rb_define_alloc_func(rb_cString, empty_str_alloc);
    rb_define_singleton_method(rb_cString, "try_convert", rb_str_s_try_convert, 1);
    rb_define_method(rb_cString, "initialize", rb_str_init, -1);
    rb_define_method(rb_cString, "initialize_copy", rb_str_replace, 1);
    rb_define_method(rb_cString, "<=>", rb_str_cmp_m, 1);
    rb_define_method(rb_cString, "==", rb_str_equal, 1);
    rb_define_method(rb_cString, "===", rb_str_equal, 1);
    rb_define_method(rb_cString, "eql?", rb_str_eql, 1);
    rb_define_method(rb_cString, "hash", rb_str_hash_m, 0);
    rb_define_method(rb_cString, "casecmp", rb_str_casecmp, 1);
    rb_define_method(rb_cString, "+", rb_str_plus, 1);
    rb_define_method(rb_cString, "*", rb_str_times, 1);
    rb_define_method(rb_cString, "%", rb_str_format_m, 1);
    rb_define_method(rb_cString, "[]", rb_str_aref_m, -1);
    rb_define_method(rb_cString, "[]=", rb_str_aset_m, -1);
    rb_define_method(rb_cString, "insert", rb_str_insert, 2);
    rb_define_method(rb_cString, "length", rb_str_length, 0);
    rb_define_method(rb_cString, "size", rb_str_length, 0);
    rb_define_method(rb_cString, "bytesize", rb_str_bytesize, 0);
    rb_define_method(rb_cString, "empty?", rb_str_empty, 0);
    rb_define_method(rb_cString, "=~", rb_str_match, 1);
    rb_define_method(rb_cString, "match", rb_str_match_m, -1);
    rb_define_method(rb_cString, "succ", rb_str_succ, 0);
    rb_define_method(rb_cString, "succ!", rb_str_succ_bang, 0);
    rb_define_method(rb_cString, "next", rb_str_succ, 0);
    rb_define_method(rb_cString, "next!", rb_str_succ_bang, 0);
    rb_define_method(rb_cString, "upto", rb_str_upto, -1);
    rb_define_method(rb_cString, "index", rb_str_index_m, -1);
    rb_define_method(rb_cString, "rindex", rb_str_rindex_m, -1);
    rb_define_method(rb_cString, "replace", rb_str_replace, 1);
    rb_define_method(rb_cString, "clear", rb_str_clear, 0);
    rb_define_method(rb_cString, "chr", rb_str_chr, 0);
    rb_define_method(rb_cString, "getbyte", rb_str_getbyte, 1);
    rb_define_method(rb_cString, "setbyte", rb_str_setbyte, 2);
    rb_define_method(rb_cString, "byteslice", rb_str_byteslice, -1);
    rb_define_method(rb_cString, "scrub", str_scrub, -1);
    rb_define_method(rb_cString, "scrub!", str_scrub_bang, -1);
    rb_define_method(rb_cString, "freeze", rb_obj_freeze, 0);

    rb_define_method(rb_cString, "to_i", rb_str_to_i, -1);
    rb_define_method(rb_cString, "to_f", rb_str_to_f, 0);
    rb_define_method(rb_cString, "to_s", rb_str_to_s, 0);
    rb_define_method(rb_cString, "to_str", rb_str_to_s, 0);
    rb_define_method(rb_cString, "inspect", rb_str_inspect, 0);
    rb_define_method(rb_cString, "dump", rb_str_dump, 0);

    rb_define_method(rb_cString, "upcase", rb_str_upcase, 0);
    rb_define_method(rb_cString, "downcase", rb_str_downcase, 0);
    rb_define_method(rb_cString, "capitalize", rb_str_capitalize, 0);
    rb_define_method(rb_cString, "swapcase", rb_str_swapcase, 0);

    rb_define_method(rb_cString, "upcase!", rb_str_upcase_bang, 0);
    rb_define_method(rb_cString, "downcase!", rb_str_downcase_bang, 0);
    rb_define_method(rb_cString, "capitalize!", rb_str_capitalize_bang, 0);
    rb_define_method(rb_cString, "swapcase!", rb_str_swapcase_bang, 0);

    rb_define_method(rb_cString, "hex", rb_str_hex, 0);
    rb_define_method(rb_cString, "oct", rb_str_oct, 0);
    rb_define_method(rb_cString, "split", rb_str_split_m, -1);
    rb_define_method(rb_cString, "lines", rb_str_lines, -1);
    rb_define_method(rb_cString, "bytes", rb_str_bytes, 0);
    rb_define_method(rb_cString, "chars", rb_str_chars, 0);
    rb_define_method(rb_cString, "codepoints", rb_str_codepoints, 0);
    rb_define_method(rb_cString, "reverse", rb_str_reverse, 0);
    rb_define_method(rb_cString, "reverse!", rb_str_reverse_bang, 0);
    rb_define_method(rb_cString, "concat", rb_str_concat, 1);
    rb_define_method(rb_cString, "<<", rb_str_concat, 1);
    rb_define_method(rb_cString, "prepend", rb_str_prepend, 1);
    rb_define_method(rb_cString, "crypt", rb_str_crypt, 1);
    rb_define_method(rb_cString, "intern", rb_str_intern, 0);
    rb_define_method(rb_cString, "to_sym", rb_str_intern, 0);
    rb_define_method(rb_cString, "ord", rb_str_ord, 0);

    rb_define_method(rb_cString, "include?", rb_str_include, 1);
    rb_define_method(rb_cString, "start_with?", rb_str_start_with, -1);
    rb_define_method(rb_cString, "end_with?", rb_str_end_with, -1);

    rb_define_method(rb_cString, "scan", rb_str_scan, 1);

    rb_define_method(rb_cString, "ljust", rb_str_ljust, -1);
    rb_define_method(rb_cString, "rjust", rb_str_rjust, -1);
    rb_define_method(rb_cString, "center", rb_str_center, -1);

    rb_define_method(rb_cString, "sub", rb_str_sub, -1);
    rb_define_method(rb_cString, "gsub", rb_str_gsub, -1);
    rb_define_method(rb_cString, "chop", rb_str_chop, 0);
    rb_define_method(rb_cString, "chomp", rb_str_chomp, -1);
    rb_define_method(rb_cString, "strip", rb_str_strip, 0);
    rb_define_method(rb_cString, "lstrip", rb_str_lstrip, 0);
    rb_define_method(rb_cString, "rstrip", rb_str_rstrip, 0);

    rb_define_method(rb_cString, "sub!", rb_str_sub_bang, -1);
    rb_define_method(rb_cString, "gsub!", rb_str_gsub_bang, -1);
    rb_define_method(rb_cString, "chop!", rb_str_chop_bang, 0);
    rb_define_method(rb_cString, "chomp!", rb_str_chomp_bang, -1);
    rb_define_method(rb_cString, "strip!", rb_str_strip_bang, 0);
    rb_define_method(rb_cString, "lstrip!", rb_str_lstrip_bang, 0);
    rb_define_method(rb_cString, "rstrip!", rb_str_rstrip_bang, 0);

    rb_define_method(rb_cString, "tr", rb_str_tr, 2);
    rb_define_method(rb_cString, "tr_s", rb_str_tr_s, 2);
    rb_define_method(rb_cString, "delete", rb_str_delete, -1);
    rb_define_method(rb_cString, "squeeze", rb_str_squeeze, -1);
    rb_define_method(rb_cString, "count", rb_str_count, -1);

    rb_define_method(rb_cString, "tr!", rb_str_tr_bang, 2);
    rb_define_method(rb_cString, "tr_s!", rb_str_tr_s_bang, 2);
    rb_define_method(rb_cString, "delete!", rb_str_delete_bang, -1);
    rb_define_method(rb_cString, "squeeze!", rb_str_squeeze_bang, -1);

    rb_define_method(rb_cString, "each_line", rb_str_each_line, -1);
    rb_define_method(rb_cString, "each_byte", rb_str_each_byte, 0);
    rb_define_method(rb_cString, "each_char", rb_str_each_char, 0);
    rb_define_method(rb_cString, "each_codepoint", rb_str_each_codepoint, 0);

    rb_define_method(rb_cString, "sum", rb_str_sum, -1);

    rb_define_method(rb_cString, "slice", rb_str_aref_m, -1);
    rb_define_method(rb_cString, "slice!", rb_str_slice_bang, -1);

    rb_define_method(rb_cString, "partition", rb_str_partition, 1);
    rb_define_method(rb_cString, "rpartition", rb_str_rpartition, 1);

    rb_define_method(rb_cString, "encoding", rb_obj_encoding, 0); /* in encoding.c */
    rb_define_method(rb_cString, "force_encoding", rb_str_force_encoding, 1);
    rb_define_method(rb_cString, "b", rb_str_b, 0);
    rb_define_method(rb_cString, "valid_encoding?", rb_str_valid_encoding_p, 0);
    rb_define_method(rb_cString, "ascii_only?", rb_str_is_ascii_only_p, 0);

    id_to_s = rb_intern("to_s");

    rb_fs = Qnil;
    rb_define_variable("$;", &rb_fs);
    rb_define_variable("$-F", &rb_fs);

    rb_cSymbol = rb_define_class("Symbol", rb_cObject);
    rb_include_module(rb_cSymbol, rb_mComparable);
    rb_undef_alloc_func(rb_cSymbol);
    rb_undef_method(CLASS_OF(rb_cSymbol), "new");
    rb_define_singleton_method(rb_cSymbol, "all_symbols", rb_sym_all_symbols, 0); /* in parse.y */

    rb_define_method(rb_cSymbol, "==", sym_equal, 1);
    rb_define_method(rb_cSymbol, "===", sym_equal, 1);
    rb_define_method(rb_cSymbol, "inspect", sym_inspect, 0);
    rb_define_method(rb_cSymbol, "to_s", rb_sym_to_s, 0);
    rb_define_method(rb_cSymbol, "id2name", rb_sym_to_s, 0);
    rb_define_method(rb_cSymbol, "intern", sym_to_sym, 0);
    rb_define_method(rb_cSymbol, "to_sym", sym_to_sym, 0);
    rb_define_method(rb_cSymbol, "to_proc", sym_to_proc, 0);
    rb_define_method(rb_cSymbol, "succ", sym_succ, 0);
    rb_define_method(rb_cSymbol, "next", sym_succ, 0);

    rb_define_method(rb_cSymbol, "<=>", sym_cmp, 1);
    rb_define_method(rb_cSymbol, "casecmp", sym_casecmp, 1);
    rb_define_method(rb_cSymbol, "=~", sym_match, 1);

    rb_define_method(rb_cSymbol, "[]", sym_aref, -1);
    rb_define_method(rb_cSymbol, "slice", sym_aref, -1);
    rb_define_method(rb_cSymbol, "length", sym_length, 0);
    rb_define_method(rb_cSymbol, "size", sym_length, 0);
    rb_define_method(rb_cSymbol, "empty?", sym_empty, 0);
    rb_define_method(rb_cSymbol, "match", sym_match, 1);

    rb_define_method(rb_cSymbol, "upcase", sym_upcase, 0);
    rb_define_method(rb_cSymbol, "downcase", sym_downcase, 0);
    rb_define_method(rb_cSymbol, "capitalize", sym_capitalize, 0);
    rb_define_method(rb_cSymbol, "swapcase", sym_swapcase, 0);

    rb_define_method(rb_cSymbol, "encoding", sym_encoding, 0);

    if (frozen_strings)
        st_foreach(frozen_strings, fstring_set_class_i, rb_cString);
}

---