text: /* vim: set ft=c nu et sw=2 fdc=2 fdm=syntax : */
  #define LUA_LIB
  #include <lua.h>
  #include <lauxlib.h>
  #include <lualib.h>
  
  
  #include <assert.h>
  #include <string.h>
  
  
  /* UTF-8 string operations */
  
  typedef unsigned int utfint;
  
  #define UTF8_BUFFSZ 8
  #define UTF8_MAX    0x7FFFFFFFu
  #define UTF8_MAXCP  0x10FFFFu
  #define iscont(p)   ((*(p) & 0xC0) == 0x80)
  
  #ifndef LUA_QL
  # define LUA_QL(x) "'" x "'"
  #endif
  
  static int utf8_invalid (utfint ch)
  { return (ch > UTF8_MAXCP || (0xD800u <= ch && ch <= 0xDFFFu)); }
  
  static size_t utf8_encode (char *buff, utfint x) {
    int n = 1;  /* number of bytes put in buffer (backwards) */
    lua_assert(x <= UTF8_MAX);
    if (x < 0x80)  /* ascii? */
      buff[UTF8_BUFFSZ - 1] = x & 0x7F;
    else {  /* need continuation bytes */
      utfint mfb = 0x3f;  /* maximum that fits in first byte */
      do {  /* add continuation bytes */
        buff[UTF8_BUFFSZ - (n++)] = 0x80 | (x & 0x3f);
        x >>= 6;  /* remove added bits */
        mfb >>= 1;  /* now there is one less bit available in first byte */
      } while (x > mfb);  /* still needs continuation byte? */
      buff[UTF8_BUFFSZ - n] = ((~mfb << 1) | x) & 0xFF;  /* add first byte */
    }
    return n;
  }
  
  static const char *utf8_decode (const char *s, utfint *val, int strict) {
    static const utfint limits[] =
    {~0u, 0x80u, 0x800u, 0x10000u, 0x200000u, 0x4000000u};
    unsigned int c = (unsigned char)s[0];
    utfint res = 0;  /* final result */
    if (c < 0x80)  /* ascii? */
      res = c;
    else {
      int count = 0;  /* to count number of continuation bytes */
      for (; c & 0x40; c <<= 1) {  /* while it needs continuation bytes... */
        unsigned int cc = (unsigned char)s[++count];  /* read next byte */
        if ((cc & 0xC0) != 0x80)  /* not a continuation byte? */
          return NULL;  /* invalid byte sequence */
        res = (res << 6) | (cc & 0x3F);  /* add lower 6 bits from cont. byte */
      }
      res |= ((utfint)(c & 0x7F) << (count * 5));  /* add first byte */
      if (count > 5 || res > UTF8_MAX || res < limits[count])
        return NULL;  /* invalid byte sequence */
      s += count;  /* skip continuation bytes read */
    }
    if (strict) {
      /* check for invalid code points; too large or surrogates */
      if (res > UTF8_MAXCP || (0xD800u <= res && res <= 0xDFFFu))
        return NULL;
    }
    if (val) *val = res;
    return s + 1;  /* +1 to include first byte */
  }
  
  static const char *utf8_prev (const char *s, const char *e) {
    while (s < e && iscont(e - 1)) --e;
    return s < e ? e - 1 : s;
  }
  
  static const char *utf8_next (const char *s, const char *e) {
    while (s < e && iscont(s + 1)) ++s;
    return s < e ? s + 1 : e;
  }
  
  static size_t utf8_length (const char *s, const char *e) {
    size_t i;
    for (i = 0; s < e; ++i)
      s = utf8_next(s, e);
    return i;
  }
  
  static const char *utf8_offset (const char *s, const char *e, lua_Integer offset, lua_Integer idx) {
    const char *p = s + offset - 1;
    if (idx >= 0) {
      while (p < e && idx > 0)
        p = utf8_next(p, e), --idx;
      return idx == 0 ? p : NULL;
    } else {
      while (s < p && idx < 0)
        p = utf8_prev(s, p), ++idx;
      return idx == 0 ? p : NULL;
    }
  }
  
  static const char *utf8_relat (const char *s, const char *e, int idx) {
    return idx >= 0 ?
      utf8_offset(s, e, 1, idx - 1) :
      utf8_offset(s, e, e-s+1, idx);
  }
  
  static int utf8_range(const char *s, const char *e, lua_Integer *i, lua_Integer *j) {
    const char *ps = utf8_relat(s, e, *i);
    const char *pe = utf8_relat(s, e, *j);
    *i = (ps ? ps : (*i > 0 ? e : s)) - s;
    *j = (pe ? utf8_next(pe, e) : (*j > 0 ? e : s)) - s;
    return *i < *j;
  }
  
  
  /* Unicode character categories */
  
  #include "unidata.h"
  
  #define table_size(t) (sizeof(t)/sizeof((t)[0]))
  
  #define utf8_categories(X) \
    X('a', alpha) \
    X('c', cntrl) \
    X('d', digit) \
    X('l', lower) \
    X('p', punct) \
    X('s', space) \
    X('t', compose) \
    X('u', upper) \
    X('x', xdigit)
  
  #define utf8_converters(X) \
    X(lower) \
    X(upper) \
    X(title) \
    X(fold)
  
  static int find_in_range (range_table *t, size_t size, utfint ch) {
    size_t begin, end;
  
    begin = 0;
    end = size;
  
    while (begin < end) {
      int mid = (begin + end) / 2;
      if (t[mid].last < ch)
        begin = mid + 1;
      else if (t[mid].first > ch)
        end = mid;
      else
        return (ch - t[mid].first) % t[mid].step == 0;
    }
  
    return 0;
  }
  
  static int convert_char (conv_table *t, size_t size, utfint ch) {
    size_t begin, end;
  
    begin = 0;
    end = size;
  
    while (begin < end) {
      int mid = (begin + end) / 2;
      if (t[mid].last < ch)
        begin = mid + 1;
      else if (t[mid].first > ch)
        end = mid;
      else if ((ch - t[mid].first) % t[mid].step == 0)
        return ch + t[mid].offset;
      else
        return ch;
    }
  
    return ch;
  }
  
  #define define_category(cls, name) static int utf8_is##name (utfint ch)\
  { return find_in_range(name##_table, table_size(name##_table), ch); }
  #define define_converter(name) static utfint utf8_to##name (utfint ch) \
  { return convert_char(to##name##_table, table_size(to##name##_table), ch); }
  utf8_categories(define_category)
  utf8_converters(define_converter)
  #undef define_category
  #undef define_converter
  
  static int utf8_isgraph (utfint ch) {
    if (find_in_range(space_table, table_size(space_table), ch))
      return 0;
    if (find_in_range(graph_table, table_size(graph_table), ch))
      return 1;
    if (find_in_range(compose_table, table_size(compose_table), ch))
      return 1;
    return 0;
  }
  
  static int utf8_isalnum (utfint ch) {
    if (find_in_range(alpha_table, table_size(alpha_table), ch))
      return 1;
    if (find_in_range(alnum_extend_table, table_size(alnum_extend_table), ch))
      return 1;
    return 0;
  }
  
  static int utf8_width (utfint ch, int ambi_is_single) {
    if (find_in_range(doublewidth_table, table_size(doublewidth_table), ch))
      return 2;
    if (find_in_range(ambiwidth_table, table_size(ambiwidth_table), ch))
      return ambi_is_single ? 1 : 2;
    if (find_in_range(compose_table, table_size(compose_table), ch))
      return 0;
    if (find_in_range(unprintable_table, table_size(unprintable_table), ch))
      return 0;
    return 1;
  }
  
  
  /* string module compatible interface */
  
  static int typeerror (lua_State *L, int idx, const char *tname)
  { return luaL_error(L, "%s expected, got %s", tname, luaL_typename(L, idx)); }
  
  static const char *check_utf8 (lua_State *L, int idx, const char **end) {
    size_t len;
    const char *s = luaL_checklstring(L, idx, &len);
    if (end) *end = s+len;
    return s;
  }
  
  static const char *to_utf8 (lua_State *L, int idx, const char **end) {
    size_t len;
    const char *s = lua_tolstring(L, idx, &len);
    if (end) *end = s+len;
    return s;
  }
  
  static const char *utf8_safe_decode (lua_State *L, const char *p, utfint *pval) {
    p = utf8_decode(p, pval, 0);
    if (p == NULL) luaL_error(L, "invalid UTF-8 code");
    return p;
  }
  
  static void add_utf8char (luaL_Buffer *b, utfint ch) {
    char buff[UTF8_BUFFSZ];
    size_t n = utf8_encode(buff, ch);
    luaL_addlstring(b, buff+UTF8_BUFFSZ-n, n);
  }
  
  static lua_Integer byte_relat (lua_Integer pos, size_t len) {
    if (pos >= 0) return pos;
    else if (0u - (size_t)pos > len) return 0;
    else return (lua_Integer)len + pos + 1;
  }
  
  static int Lutf8_len (lua_State *L) {
    size_t len, n;
    const char *s = luaL_checklstring(L, 1, &len), *p, *e;
    lua_Integer posi = byte_relat(luaL_optinteger(L, 2, 1), len);
    lua_Integer pose = byte_relat(luaL_optinteger(L, 3, -1), len);
    int lax = lua_toboolean(L, 4);
    luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 2,
                     "initial position out of string");
    luaL_argcheck(L, --pose < (lua_Integer)len, 3,
                     "final position out of string");
    for (n = 0, p=s+posi, e=s+pose+1; p < e; ++n) {
      if (lax)
        p = utf8_next(p, e);
      else {
        utfint ch;
        const char *np = utf8_decode(p, &ch, !lax);
        if (np == NULL || utf8_invalid(ch)) {
          lua_pushnil(L);
          lua_pushinteger(L, p - s + 1);
          return 2;
        }
        p = np;
      }
    }
    lua_pushinteger(L, n);
    return 1;
  }
  
  static int Lutf8_sub (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    lua_Integer posi = luaL_checkinteger(L, 2);
    lua_Integer pose = luaL_optinteger(L, 3, -1);
    if (utf8_range(s, e, &posi, &pose))
      lua_pushlstring(L, s+posi, pose-posi);
    else
      lua_pushliteral(L, "");
    return 1;
  }
  
  static int Lutf8_reverse (lua_State *L) {
    luaL_Buffer b;
    const char *prev, *pprev, *ends, *e, *s = check_utf8(L, 1, &e);
    int lax = lua_toboolean(L, 2);
    luaL_buffinit(L, &b);
    if (lax) {
      for (prev = e; s < prev; e = prev) {
        prev = utf8_prev(s, prev);
        luaL_addlstring(&b, prev, e-prev);
      }
    } else {
      for (prev = e; s < prev; prev = pprev) {
        utfint code;
        ends = utf8_safe_decode(L, pprev = utf8_prev(s, prev), &code);
        assert(ends == prev);
        if (utf8_invalid(code))
          return luaL_error(L, "invalid UTF-8 code");
        if (!utf8_iscompose(code)) {
          luaL_addlstring(&b, pprev, e-pprev);
          e = pprev;
        }
      }
    }
    luaL_pushresult(&b);
    return 1;
  }
  
  static int Lutf8_byte (lua_State *L) {
    size_t n = 0;
    const char *e, *s = check_utf8(L, 1, &e);
    lua_Integer posi = luaL_optinteger(L, 2, 1);
    lua_Integer pose = luaL_optinteger(L, 3, posi);
    if (utf8_range(s, e, &posi, &pose)) {
      for (e = s + pose, s = s + posi; s < e; ++n) {
        utfint ch;
        s = utf8_safe_decode(L, s, &ch);
        lua_pushinteger(L, ch);
      }
    }
    return n;
  }
  
  static int Lutf8_codepoint (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    size_t len = e-s;
    lua_Integer posi = byte_relat(luaL_optinteger(L, 2, 1), len);
    lua_Integer pose = byte_relat(luaL_optinteger(L, 3, posi), len);
    int lax = lua_toboolean(L, 4);
    int n;
    const char *se;
    luaL_argcheck(L, posi >= 1, 2, "out of range");
    luaL_argcheck(L, pose <= (lua_Integer)len, 3, "out of range");
    if (posi > pose) return 0;  /* empty interval; return no values */
    if (pose - posi >= INT_MAX)  /* (lua_Integer -> int) overflow? */
      return luaL_error(L, "string slice too long");
    n = (int)(pose -  posi + 1);
    luaL_checkstack(L, n, "string slice too long");
    n = 0;  /* count the number of returns */
    se = s + pose;  /* string end */
    for (n = 0, s += posi - 1; s < se;) {
      utfint code;
      s = utf8_safe_decode(L, s, &code);
      if (!lax && utf8_invalid(code))
        return luaL_error(L, "invalid UTF-8 code");
      lua_pushinteger(L, code);
      n++;
    }
    return n;
  }
  
  static int Lutf8_char (lua_State *L) {
    int i, n = lua_gettop(L); /* number of arguments */
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    for (i = 1; i <= n; ++i) {
      lua_Integer code = luaL_checkinteger(L, i);
      luaL_argcheck(L, code <= UTF8_MAXCP, i, "value out of range");
      add_utf8char(&b, code);
    }
    luaL_pushresult(&b);
    return 1;
  }
  
  #define bind_converter(name)                                   \
  static int Lutf8_##name (lua_State *L) {                        \
    int t = lua_type(L, 1);                                      \
    if (t == LUA_TNUMBER)                                        \
      lua_pushinteger(L, utf8_to##name(lua_tointeger(L, 1)));    \
    else if (t == LUA_TSTRING) {                                 \
      luaL_Buffer b;                                             \
      const char *e, *s = to_utf8(L, 1, &e);                     \
      luaL_buffinit(L, &b);                                      \
      while (s < e) {                                            \
        utfint ch;                                               \
        s = utf8_safe_decode(L, s, &ch);                         \
        add_utf8char(&b, utf8_to##name(ch));                     \
      }                                                          \
      luaL_pushresult(&b);                                       \
    }                                                            \
    else return typeerror(L, 1, "number/string");                \
    return 1;                                                    \
  }
  utf8_converters(bind_converter)
  #undef bind_converter
  
  
  /* unicode extra interface */
  
  static const char *parse_escape (lua_State *L, const char *s, const char *e, int hex, utfint *pch) {
    utfint code = 0;
    int in_bracket = 0;
    if (*s == '{') ++s, in_bracket = 1;
    for (; s < e; ++s) {
      utfint ch = (unsigned char)*s;
      if (ch >= '0' && ch <= '9') ch = ch - '0';
      else if (hex && ch >= 'A' && ch <= 'F') ch = 10 + (ch - 'A');
      else if (hex && ch >= 'a' && ch <= 'f') ch = 10 + (ch - 'a');
      else if (!in_bracket) break;
      else if (ch == '}')   { ++s; break; }
      else luaL_error(L, "invalid escape '%c'", ch);
      code *= hex ? 16 : 10;
      code += ch;
    }
    *pch = code;
    return s;
  }
  
  static int Lutf8_escape (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    while (s < e) {
      utfint ch;
      s = utf8_safe_decode(L, s, &ch);
      if (ch == '%') {
        int hex = 0;
        switch (*s) {
        case '0': case '1': case '2': case '3':
        case '4': case '5': case '6': case '7':
        case '8': case '9': case '{':
          break;
        case 'x': case 'X': hex = 1; /* FALLTHOUGH */
        case 'u': case 'U': if (s+1 < e) { ++s; break; }
                              /* FALLTHOUGH */
        default:
          s = utf8_safe_decode(L, s, &ch);
          goto next;
        }
        s = parse_escape(L, s, e, hex, &ch);
      }
  next:
      add_utf8char(&b, ch);
    }
    luaL_pushresult(&b);
    return 1;
  }
  
  static int Lutf8_insert (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    size_t sublen;
    const char *subs;
    luaL_Buffer b;
    int nargs = 2;
    const char *first = e;
    if (lua_type(L, 2) == LUA_TNUMBER) {
      int idx = (int)lua_tointeger(L, 2);
      if (idx != 0) first = utf8_relat(s, e, idx);
      luaL_argcheck(L, first, 2, "invalid index");
      ++nargs;
    }
    subs = luaL_checklstring(L, nargs, &sublen);
    luaL_buffinit(L, &b);
    luaL_addlstring(&b, s, first-s);
    luaL_addlstring(&b, subs, sublen);
    luaL_addlstring(&b, first, e-first);
    luaL_pushresult(&b);
    return 1;
  }
  
  static int Lutf8_remove (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    lua_Integer posi = luaL_optinteger(L, 2, -1);
    lua_Integer pose = luaL_optinteger(L, 3, -1);
    if (!utf8_range(s, e, &posi, &pose))
      lua_settop(L, 1);
    else {
      luaL_Buffer b;
      luaL_buffinit(L, &b);
      luaL_addlstring(&b, s, posi);
      luaL_addlstring(&b, s+pose, e-s-pose);
      luaL_pushresult(&b);
    }
    return 1;
  }
  
  static int push_offset (lua_State *L, const char *s, const char *e, lua_Integer offset, lua_Integer idx) {
    utfint ch = 0;
    const char *p;
    if (idx != 0)
      p = utf8_offset(s, e, offset, idx);
    else if (p = s+offset-1, iscont(p))
      p = utf8_prev(s, p);
    if (p == NULL || p == e) return 0;
    utf8_decode(p, &ch, 0);
    lua_pushinteger(L, p-s+1);
    lua_pushinteger(L, ch);
    return 2;
  }
  
  static int Lutf8_charpos (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    lua_Integer offset = 1;
    if (lua_isnoneornil(L, 3)) {
        lua_Integer idx = luaL_optinteger(L, 2, 0);
        if (idx > 0) --idx;
        else if (idx < 0) offset = e-s+1;
        return push_offset(L, s, e, offset, idx);
    }
    offset = byte_relat(luaL_optinteger(L, 2, 1), e-s);
    if (offset < 1) offset = 1;
    return push_offset(L, s, e, offset, luaL_checkinteger(L, 3));
  }
  
  static int Lutf8_offset (lua_State *L) {
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer n  = luaL_checkinteger(L, 2);
    lua_Integer posi = (n >= 0) ? 1 : len + 1;
    posi = byte_relat(luaL_optinteger(L, 3, posi), len);
    luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 3,
                     "position out of range");
    if (n == 0) {
      /* find beginning of current byte sequence */
      while (posi > 0 && iscont(s + posi)) posi--;
    } else {
      if (iscont(s + posi))
        return luaL_error(L, "initial position is a continuation byte");
      if (n < 0) {
         while (n < 0 && posi > 0) {  /* move back */
           do {  /* find beginning of previous character */
             posi--;
           } while (posi > 0 && iscont(s + posi));
           n++;
         }
       } else {
         n--;  /* do not move for 1st character */
         while (n > 0 && posi < (lua_Integer)len) {
           do {  /* find beginning of next character */
             posi++;
           } while (iscont(s + posi));  /* (cannot pass final '\0') */
           n--;
         }
       }
    }
    if (n == 0)  /* did it find given character? */
      lua_pushinteger(L, posi + 1);
    else  /* no such character */
      lua_pushnil(L);
    return 1;
  }
  
  static int Lutf8_next (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    lua_Integer offset = byte_relat(luaL_optinteger(L, 2, 1), e-s);
    lua_Integer idx = luaL_optinteger(L, 3, !lua_isnoneornil(L, 2));
    return push_offset(L, s, e, offset, idx);
  }
  
  static int iter_aux (lua_State *L, int strict) {
    const char *e, *s = check_utf8(L, 1, &e);
    int n = lua_tointeger(L, 2);
    const char *p = n <= 0 ? s : utf8_next(s+n-1, e);
    if (p < e) {
      utfint code;
      utf8_safe_decode(L, p, &code);
      if (strict && utf8_invalid(code))
        return luaL_error(L, "invalid UTF-8 code");
      lua_pushinteger(L, p-s+1);
      lua_pushinteger(L, code);
      return 2;
    }
    return 0;  /* no more codepoints */
  }
  
  static int iter_auxstrict (lua_State *L) { return iter_aux(L, 1); }
  static int iter_auxlax (lua_State *L) { return iter_aux(L, 0); }
  
  static int Lutf8_codes (lua_State *L) {
    int lax = lua_toboolean(L, 2);
    luaL_checkstring(L, 1);
    lua_pushcfunction(L, lax ? iter_auxlax : iter_auxstrict);
    lua_pushvalue(L, 1);
    lua_pushinteger(L, 0);
    return 3;
  }
  
  static int Lutf8_width (lua_State *L) {
    int t = lua_type(L, 1);
    int ambi_is_single = !lua_toboolean(L, 2);
    int default_width = luaL_optinteger(L, 3, 0);
    if (t == LUA_TNUMBER) {
      size_t chwidth = utf8_width(lua_tointeger(L, 1), ambi_is_single);
      if (chwidth == 0) chwidth = default_width;
      lua_pushinteger(L, (lua_Integer)chwidth);
    } else if (t != LUA_TSTRING)
      return typeerror(L, 1, "number/string");
    else {
      const char *e, *s = to_utf8(L, 1, &e);
      int width = 0;
      while (s < e) {
        utfint ch;
        int chwidth;
        s = utf8_safe_decode(L, s, &ch);
        chwidth = utf8_width(ch, ambi_is_single);
        width += chwidth == 0 ? default_width : chwidth;
      }
      lua_pushinteger(L, (lua_Integer)width);
    }
    return 1;
  }
  
  static int Lutf8_widthindex (lua_State *L) {
    const char *e, *s = check_utf8(L, 1, &e);
    int width = luaL_checkinteger(L, 2);
    int ambi_is_single = !lua_toboolean(L, 3);
    int default_width = luaL_optinteger(L, 4, 0);
    size_t idx = 1;
    while (s < e) {
      utfint ch;
      size_t chwidth;
      s = utf8_safe_decode(L, s, &ch);
      chwidth = utf8_width(ch, ambi_is_single);
      if (chwidth == 0) chwidth = default_width;
      width -= chwidth;
      if (width <= 0) {
        lua_pushinteger(L, idx);
        lua_pushinteger(L, width + chwidth);
        lua_pushinteger(L, chwidth);
        return 3;
      }
      ++idx;
    }
    lua_pushinteger(L, (lua_Integer)idx);
    return 1;
  }
  
  static int Lutf8_ncasecmp (lua_State *L) {
    const char *e1, *s1 = check_utf8(L, 1, &e1);
    const char *e2, *s2 = check_utf8(L, 2, &e2);
    while (s1 < e1 || s2 < e2) {
      utfint ch1 = 0, ch2 = 0;
      if (s1 == e1)
        ch2 = 1;
      else if (s2 == e2)
        ch1 = 1;
      else {
        s1 = utf8_safe_decode(L, s1, &ch1);
        s2 = utf8_safe_decode(L, s2, &ch2);
        ch1 = utf8_tofold(ch1);
        ch2 = utf8_tofold(ch2);
      }
      if (ch1 != ch2) {
        lua_pushinteger(L, ch1 > ch2 ? 1 : -1);
        return 1;
      }
    }
    lua_pushinteger(L, 0);
    return 1;
  }
  
  
  /* utf8 pattern matching implement */
  
  #ifndef   LUA_MAXCAPTURES
  # define  LUA_MAXCAPTURES  32
  #endif /* LUA_MAXCAPTURES */
  
  #define CAP_UNFINISHED (-1)
  #define CAP_POSITION   (-2)
  
  
  typedef struct MatchState {
    int matchdepth;  /* control for recursive depth (to avoid C stack overflow) */
    const char *src_init;  /* init of source string */
    const char *src_end;  /* end ('\0') of source string */
    const char *p_end;  /* end ('\0') of pattern */
    lua_State *L;
    int level;  /* total number of captures (finished or unfinished) */
    struct {
      const char *init;
      ptrdiff_t len;
    } capture[LUA_MAXCAPTURES];
  } MatchState;
  
  /* recursive function */
  static const char *match (MatchState *ms, const char *s, const char *p);
  
  /* maximum recursion depth for 'match' */
  #if !defined(MAXCCALLS)
  #define MAXCCALLS       200
  #endif
  
  #define L_ESC           '%'
  #define SPECIALS        "^$*+?.([%-"
  
  static int check_capture (MatchState *ms, int l) {
    l -= '1';
    if (l < 0 || l >= ms->level || ms->capture[l].len == CAP_UNFINISHED)
      return luaL_error(ms->L, "invalid capture index %%%d", l + 1);
    return l;
  }
  
  static int capture_to_close (MatchState *ms) {
    int level = ms->level;
    while (--level >= 0)
      if (ms->capture[level].len == CAP_UNFINISHED) return level;
    return luaL_error(ms->L, "invalid pattern capture");
  }
  
  static const char *classend (MatchState *ms, const char *p) {
    utfint ch;
    p = utf8_safe_decode(ms->L, p, &ch);
    switch (ch) {
      case L_ESC: {
        if (p == ms->p_end)
          luaL_error(ms->L, "malformed pattern (ends with " LUA_QL("%%") ")");
        return utf8_next(p, ms->p_end);
      }
      case '[': {
        if (*p == '^') p++;
        do {  /* look for a `]' */
          if (p == ms->p_end)
            luaL_error(ms->L, "malformed pattern (missing " LUA_QL("]") ")");
          if (*(p++) == L_ESC && p < ms->p_end)
            p++;  /* skip escapes (e.g. `%]') */
        } while (*p != ']');
        return p+1;
      }
      default: {
        return p;
      }
    }
  }
  
  static int match_class (utfint c, utfint cl) {
    int res;
    switch (utf8_tolower(cl)) {
  #define X(cls, name) case cls: res = utf8_is##name(c); break;
      utf8_categories(X)
  #undef  X
      case 'g' : res = utf8_isgraph(c); break;
      case 'w' : res = utf8_isalnum(c); break;
      case 'z' : res = (c == 0); break;  /* deprecated option */
      default: return (cl == c);
    }
    return (utf8_islower(cl) ? res : !res);
  }
  
  static int matchbracketclass (MatchState *ms, utfint c, const char *p, const char *ec) {
    int sig = 1;
    assert(*p == '[');
    if (*++p == '^') {
      sig = 0;
      p++;  /* skip the `^' */
    }
    while (p < ec) {
      utfint ch;
      p = utf8_safe_decode(ms->L, p, &ch);
      if (ch == L_ESC) {
        p = utf8_safe_decode(ms->L, p, &ch);
        if (match_class(c, ch))
          return sig;
      } else {
        utfint next;
        const char *np = utf8_safe_decode(ms->L, p, &next);
        if (next == '-' && np < ec) {
          p = utf8_safe_decode(ms->L, np, &next);
          if (ch <= c && c <= next)
            return sig;
        }
        else if (ch == c) return sig;
      }
    }
    return !sig;
  }
  
  static int singlematch (MatchState *ms, const char *s, const char *p, const char *ep) {
    if (s >= ms->src_end)
      return 0;
    else {
      utfint ch, pch;
      utf8_safe_decode(ms->L, s, &ch);
      p = utf8_safe_decode(ms->L, p, &pch);
      switch (pch) {
        case '.': return 1;  /* matches any char */
        case L_ESC: utf8_safe_decode(ms->L, p, &pch);
                    return match_class(ch, pch);
        case '[': return matchbracketclass(ms, ch, p-1, ep-1);
        default:  return pch == ch;
      }
    }
  }
  
  static const char *matchbalance (MatchState *ms, const char *s, const char **p) {
    utfint ch, begin, end;
    *p = utf8_safe_decode(ms->L, *p, &begin);
    if (*p >= ms->p_end)
      luaL_error(ms->L, "malformed pattern "
                        "(missing arguments to " LUA_QL("%%b") ")");
    *p = utf8_safe_decode(ms->L, *p, &end);
    s = utf8_safe_decode(ms->L, s, &ch);
    if (ch != begin) return NULL;
    else {
      int cont = 1;
      while (s < ms->src_end) {
        s = utf8_safe_decode(ms->L, s, &ch);
        if (ch == end) {
          if (--cont == 0) return s;
        }
        else if (ch == begin) cont++;
      }
    }
    return NULL;  /* string ends out of balance */
  }
  
  static const char *max_expand (MatchState *ms, const char *s, const char *p, const char *ep) {
    const char *m = s; /* matched end of single match p */
    while (singlematch(ms, m, p, ep))
      m = utf8_next(m, ms->src_end);
    /* keeps trying to match with the maximum repetitions */
    while (s <= m) {
      const char *res = match(ms, m, ep+1);
      if (res) return res;
      /* else didn't match; reduce 1 repetition to try again */
      if (s == m) break;
      m = utf8_prev(s, m);
    }
    return NULL;
  }
  
  static const char *min_expand (MatchState *ms, const char *s, const char *p, const char *ep) {
    for (;;) {
      const char *res = match(ms, s, ep+1);
      if (res != NULL)
        return res;
      else if (singlematch(ms, s, p, ep))
        s = utf8_next(s, ms->src_end);  /* try with one more repetition */
      else return NULL;
    }
  }
  
  static const char *start_capture (MatchState *ms, const char *s, const char *p, int what) {
    const char *res;
    int level = ms->level;
    if (level >= LUA_MAXCAPTURES) luaL_error(ms->L, "too many captures");
    ms->capture[level].init = s;
    ms->capture[level].len = what;
    ms->level = level+1;
    if ((res=match(ms, s, p)) == NULL)  /* match failed? */
      ms->level--;  /* undo capture */
    return res;
  }
  
  static const char *end_capture (MatchState *ms, const char *s, const char *p) {
    int l = capture_to_close(ms);
    const char *res;
    ms->capture[l].len = s - ms->capture[l].init;  /* close capture */
    if ((res = match(ms, s, p)) == NULL)  /* match failed? */
      ms->capture[l].len = CAP_UNFINISHED;  /* undo capture */
    return res;
  }
  
  static const char *match_capture (MatchState *ms, const char *s, int l) {
    size_t len;
    l = check_capture(ms, l);
    len = ms->capture[l].len;
    if ((size_t)(ms->src_end-s) >= len &&
        memcmp(ms->capture[l].init, s, len) == 0)
      return s+len;
    else return NULL;
  }
  
  static const char *match (MatchState *ms, const char *s, const char *p) {
    if (ms->matchdepth-- == 0)
      luaL_error(ms->L, "pattern too complex");
    init: /* using goto's to optimize tail recursion */
    if (p != ms->p_end) {  /* end of pattern? */
      utfint ch;
      utf8_safe_decode(ms->L, p, &ch);
      switch (ch) {
        case '(': {  /* start capture */
          if (*(p + 1) == ')')  /* position capture? */
            s = start_capture(ms, s, p + 2, CAP_POSITION);
          else
            s = start_capture(ms, s, p + 1, CAP_UNFINISHED);
          break;
        }
        case ')': {  /* end capture */
          s = end_capture(ms, s, p + 1);
          break;
        }
        case '$': {
          if ((p + 1) != ms->p_end)  /* is the `$' the last char in pattern? */
            goto dflt;  /* no; go to default */
          s = (s == ms->src_end) ? s : NULL;  /* check end of string */
          break;
        }
        case L_ESC: {  /* escaped sequence not in the format class[*+?-]? */
          const char *prev_p = p;
          p = utf8_safe_decode(ms->L, p+1, &ch);
          switch (ch) {
            case 'b': {  /* balanced string? */
              s = matchbalance(ms, s, &p);
              if (s != NULL)
                goto init;  /* return match(ms, s, p + 4); */
              /* else fail (s == NULL) */
              break;
            }
            case 'f': {  /* frontier? */
              const char *ep; utfint previous = 0, current = 0;
              if (*p != '[')
                luaL_error(ms->L, "missing " LUA_QL("[") " after "
                                   LUA_QL("%%f") " in pattern");
              ep = classend(ms, p);  /* points to what is next */
              if (s != ms->src_init)
                utf8_decode(utf8_prev(ms->src_init, s), &previous, 0);
              if (s != ms->src_end)
                utf8_decode(s, &current, 0);
              if (!matchbracketclass(ms, previous, p, ep - 1) &&
                   matchbracketclass(ms, current, p, ep - 1)) {
                p = ep; goto init;  /* return match(ms, s, ep); */
              }
              s = NULL;  /* match failed */
              break;
            }
            case '0': case '1': case '2': case '3':
            case '4': case '5': case '6': case '7':
            case '8': case '9': {  /* capture results (%0-%9)? */
              s = match_capture(ms, s, ch);
              if (s != NULL) goto init;  /* return match(ms, s, p + 2) */
              break;
            }
            default: p = prev_p; goto dflt;
          }
          break;
        }
        default: dflt: {  /* pattern class plus optional suffix */
          const char *ep = classend(ms, p);  /* points to optional suffix */
          /* does not match at least once? */
          if (!singlematch(ms, s, p, ep)) {
            if (*ep == '*' || *ep == '?' || *ep == '-') {  /* accept empty? */
              p = ep + 1; goto init;  /* return match(ms, s, ep + 1); */
            } else  /* '+' or no suffix */
              s = NULL;  /* fail */
          } else {  /* matched once */
            const char *next_s = utf8_next(s, ms->src_end);
            switch (*ep) {  /* handle optional suffix */
              case '?': {  /* optional */
                const char *res;
                const char *next_ep = utf8_next(ep, ms->p_end);
                if ((res = match(ms, next_s, next_ep)) != NULL)
                  s = res;
                else {
                  p = next_ep; goto init;  /* else return match(ms, s, ep + 1); */
                }
                break;
              }
              case '+':  /* 1 or more repetitions */
                s = next_s;  /* 1 match already done */
                /* go through */
              case '*':  /* 0 or more repetitions */
                s = max_expand(ms, s, p, ep);
                break;
              case '-':  /* 0 or more repetitions (minimum) */
                s = min_expand(ms, s, p, ep);
                break;
              default:  /* no suffix */
                s = next_s; p = ep; goto init;  /* return match(ms, s + 1, ep); */
            }
          }
          break;
        }
      }
    }
    ms->matchdepth++;
    return s;
  }
  
  static const char *lmemfind (const char *s1, size_t l1, const char *s2, size_t l2) {
    if (l2 == 0) return s1;  /* empty strings are everywhere */
    else if (l2 > l1) return NULL;  /* avoids a negative `l1' */
    else {
      const char *init;  /* to search for a `*s2' inside `s1' */
      l2--;  /* 1st char will be checked by `memchr' */
      l1 = l1-l2;  /* `s2' cannot be found after that */
      while (l1 > 0 && (init = (const char *)memchr(s1, *s2, l1)) != NULL) {
        init++;   /* 1st char is already checked */
        if (memcmp(init, s2+1, l2) == 0)
          return init-1;
        else {  /* correct `l1' and `s1' to try again */
          l1 -= init-s1;
          s1 = init;
        }
      }
      return NULL;  /* not found */
    }
  }
  
  static int get_index (const char *p, const char *s, const char *e) {
      int idx;
      for (idx = 0; s < e && s < p; ++idx)
          s = utf8_next(s, e);
      return s == p ? idx : idx - 1;
  }
  
  static void push_onecapture (MatchState *ms, int i, const char *s, const char *e) {
    if (i >= ms->level) {
      if (i == 0)  /* ms->level == 0, too */
        lua_pushlstring(ms->L, s, e - s);  /* add whole match */
      else
        luaL_error(ms->L, "invalid capture index");
    } else {
      ptrdiff_t l = ms->capture[i].len;
      if (l == CAP_UNFINISHED) luaL_error(ms->L, "unfinished capture");
      if (l == CAP_POSITION) {
        int idx = get_index(ms->capture[i].init, ms->src_init, ms->src_end);
        lua_pushinteger(ms->L, idx+1);
      } else
        lua_pushlstring(ms->L, ms->capture[i].init, l);
    }
  }
  
  static int push_captures (MatchState *ms, const char *s, const char *e) {
    int i;
    int nlevels = (ms->level == 0 && s) ? 1 : ms->level;
    luaL_checkstack(ms->L, nlevels, "too many captures");
    for (i = 0; i < nlevels; i++)
      push_onecapture(ms, i, s, e);
    return nlevels;  /* number of strings pushed */
  }
  
  /* check whether pattern has no special characters */
  static int nospecials (const char *p, const char * ep) {
    while (p < ep) {
      if (strpbrk(p, SPECIALS))
        return 0;  /* pattern has a special character */
      p += strlen(p) + 1;  /* may have more after \0 */
    }
    return 1;  /* no special chars found */
  }
  
  
  /* utf8 pattern matching interface */
  
  static int find_aux (lua_State *L, int find) {
    const char *es, *s = check_utf8(L, 1, &es);
    const char *ep, *p = check_utf8(L, 2, &ep);
    lua_Integer idx = luaL_optinteger(L, 3, 1);
    const char *init;
    init = utf8_relat(s, es, idx);
    if (init == NULL) {
      if (idx > 0) {
        lua_pushnil(L);  /* cannot find anything */
        return 1;
      }
      init = s;
    }
    /* explicit request or no special characters? */
    if (find && (lua_toboolean(L, 4) || nospecials(p, ep))) {
      /* do a plain search */
      const char *s2 = lmemfind(init, es-init, p, ep-p);
      if (s2) {
        const char *e2 = s2 + (ep - p);
        if (iscont(e2)) e2 = utf8_next(e2, es);
        lua_pushinteger(L, idx = get_index(s2, s, es) + 1);
        lua_pushinteger(L, idx + get_index(e2, s2, es) - 1);
        return 2;
      }
    } else {
      MatchState ms;
      int anchor = (*p == '^');
      if (anchor) p++;  /* skip anchor character */
      if (idx < 0) idx += utf8_length(s, es)+1; /* TODO not very good */
      ms.L = L;
      ms.matchdepth = MAXCCALLS;
      ms.src_init = s;
      ms.src_end = es;
      ms.p_end = ep;
      do {
        const char *res;
        ms.level = 0;
        assert(ms.matchdepth == MAXCCALLS);
        if ((res=match(&ms, init, p)) != NULL) {
          if (find) {
            lua_pushinteger(L, idx);  /* start */
            lua_pushinteger(L, idx + utf8_length(init, res) - 1);   /* end */
            return push_captures(&ms, NULL, 0) + 2;
          } else
            return push_captures(&ms, init, res);
        }
        if (init == es) break;
        idx += 1;
        init = utf8_next(init, es);
      } while (init <= es && !anchor);
    }
    lua_pushnil(L);  /* not found */
    return 1;
  }
  
  static int Lutf8_find (lua_State *L) { return find_aux(L, 1); }
  static int Lutf8_match (lua_State *L) { return find_aux(L, 0); }
  
  static int gmatch_aux (lua_State *L) {
    MatchState ms;
    const char *es, *s = check_utf8(L, lua_upvalueindex(1), &es);
    const char *ep, *p = check_utf8(L, lua_upvalueindex(2), &ep);
    const char *src;
    ms.L = L;
    ms.matchdepth = MAXCCALLS;
    ms.src_init = s;
    ms.src_end = es;
    ms.p_end = ep;
    for (src = s + (size_t)lua_tointeger(L, lua_upvalueindex(3));
         src <= ms.src_end;
         src = utf8_next(src, ms.src_end)) {
      const char *e;
      ms.level = 0;
      assert(ms.matchdepth == MAXCCALLS);
      if ((e = match(&ms, src, p)) != NULL) {
        lua_Integer newstart = e-s;
        if (e == src) newstart++;  /* empty match? go at least one position */
        lua_pushinteger(L, newstart);
        lua_replace(L, lua_upvalueindex(3));
        return push_captures(&ms, src, e);
      }
      if (src == ms.src_end) break;
    }
    return 0;  /* not found */
  }
  
  static int Lutf8_gmatch (lua_State *L) {
    luaL_checkstring(L, 1);
    luaL_checkstring(L, 2);
    lua_settop(L, 2);
    lua_pushinteger(L, 0);
    lua_pushcclosure(L, gmatch_aux, 3);
    return 1;
  }
  
  static void add_s (MatchState *ms, luaL_Buffer *b, const char *s, const char *e) {
    const char *new_end, *news = to_utf8(ms->L, 3, &new_end);
    while (news < new_end) {
      utfint ch;
      news = utf8_safe_decode(ms->L, news, &ch);
      if (ch != L_ESC)
        add_utf8char(b, ch);
      else {
        news = utf8_safe_decode(ms->L, news, &ch); /* skip ESC */
        if (!utf8_isdigit(ch)) {
          if (ch != L_ESC)
            luaL_error(ms->L, "invalid use of " LUA_QL("%c")
                " in replacement string", L_ESC);
          add_utf8char(b, ch);
        } else if (ch == '0')
          luaL_addlstring(b, s, e-s);
        else {
          push_onecapture(ms, ch-'1', s, e);
          luaL_addvalue(b);  /* add capture to accumulated result */
        }
      }
    }
  }
  
  static void add_value (MatchState *ms, luaL_Buffer *b, const char *s, const char *e, int tr) {
    lua_State *L = ms->L;
    switch (tr) {
      case LUA_TFUNCTION: {
        int n;
        lua_pushvalue(L, 3);
        n = push_captures(ms, s, e);
        lua_call(L, n, 1);
        break;
      }
      case LUA_TTABLE: {
        push_onecapture(ms, 0, s, e);
        lua_gettable(L, 3);
        break;
      }
      default: {  /* LUA_TNUMBER or LUA_TSTRING */
        add_s(ms, b, s, e);
        return;
      }
    }
    if (!lua_toboolean(L, -1)) {  /* nil or false? */
      lua_pop(L, 1);
      lua_pushlstring(L, s, e - s);  /* keep original text */
    } else if (!lua_isstring(L, -1))
      luaL_error(L, "invalid replacement value (a %s)", luaL_typename(L, -1));
    luaL_addvalue(b);  /* add result to accumulator */
  }
  
  static int Lutf8_gsub (lua_State *L) {
    const char *es, *s = check_utf8(L, 1, &es);
    const char *ep, *p = check_utf8(L, 2, &ep);
    int tr = lua_type(L, 3);
    lua_Integer max_s = luaL_optinteger(L, 4, (es-s)+1);
    int anchor = (*p == '^');
    lua_Integer n = 0;
    MatchState ms;
    luaL_Buffer b;
    luaL_argcheck(L, tr == LUA_TNUMBER || tr == LUA_TSTRING ||
                     tr == LUA_TFUNCTION || tr == LUA_TTABLE, 3,
                        "string/function/table expected");
    luaL_buffinit(L, &b);
    if (anchor) p++;  /* skip anchor character */
    ms.L = L;
    ms.matchdepth = MAXCCALLS;
    ms.src_init = s;
    ms.src_end = es;
    ms.p_end = ep;
    while (n < max_s) {
      const char *e;
      ms.level = 0;
      assert(ms.matchdepth == MAXCCALLS);
      e = match(&ms, s, p);
      if (e) {
        n++;
        add_value(&ms, &b, s, e, tr);
      }
      if (e && e > s) /* non empty match? */
        s = e;  /* skip it */
      else if (s < es) {
        utfint ch;
        s = utf8_safe_decode(L, s, &ch);
        add_utf8char(&b, ch);
      } else break;
      if (anchor) break;
    }
    luaL_addlstring(&b, s, es-s);
    luaL_pushresult(&b);
    lua_pushinteger(L, n);  /* number of substitutions */
    return 2;
  }
  
  
  /* lua module import interface */
  
  #if LUA_VERSION_NUM >= 502
  static const char UTF8PATT[] = "[\0-\x7F\xC2-\xF4][\x80-\xBF]*";
  #else
  static const char UTF8PATT[] = "[%z\1-\x7F\xC2-\xF4][\x80-\xBF]*";
  #endif
  
  LUALIB_API int luaopen_utf8 (lua_State *L) {
    luaL_Reg libs[] = {
  #define ENTRY(name) { #name, Lutf8_##name }
      ENTRY(offset),
      ENTRY(codes),
      ENTRY(codepoint),
  
      ENTRY(len),
      ENTRY(sub),
      ENTRY(reverse),
      ENTRY(lower),
      ENTRY(upper),
      ENTRY(title),
      ENTRY(fold),
      ENTRY(byte),
      ENTRY(char),
      ENTRY(escape),
      ENTRY(insert),
      ENTRY(remove),
      ENTRY(charpos),
      ENTRY(next),
      ENTRY(width),
      ENTRY(widthindex),
      ENTRY(ncasecmp),
      ENTRY(find),
      ENTRY(gmatch),
      ENTRY(gsub),
      ENTRY(match),
  #undef  ENTRY
      { NULL, NULL }
    };
  
  #if LUA_VERSION_NUM >= 502
    luaL_newlib(L, libs);
  #else
    lua_createtable(L, 0, sizeof(libs)/sizeof(libs[0]));
    luaL_register(L, NULL, libs);
  #endif
  
    lua_pushlstring(L, UTF8PATT, sizeof(UTF8PATT)-1);
    lua_setfield(L, -2, "charpattern");
  
    return 1;
  }
  
  /* win32cc: flags+='-Wall -Wextra -s -O2 -mdll -DLUA_BUILD_AS_DLL'
   * win32cc: libs+='-llua53.dll' output='lua-utf8.dll'
   * win32cc: run='lua.exe test.lua'
   * maccc: run='lua -- test_compat.lua'
   * maccc: flags+='-g --coverage -bundle -undefined dynamic_lookup' output='lua-utf8.so' */
  
  