text: /*
  ** $Id: lutf8lib.c,v 1.16.1.1 2017/04/19 17:29:57 roberto Exp $
  ** Standard library for UTF-8 manipulation
  ** See Copyright Notice in lua.h
  */
  
  #define lutf8lib_c
  #define LUA_LIB
  
  #include "lprefix.h"
  
  
  #include <assert.h>
  #include <limits.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "lua.h"
  
  #include "lauxlib.h"
  #include "lualib.h"
  
  #define MAXUNICODE	0x10FFFF
  
  #define iscont(p)	((*(p) & 0xC0) == 0x80)
  
  
  /* from strlib */
  /* translate a relative string position: negative means back from end */
  static lua_Integer u_posrelat (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;
  }
  
  
  /*
  ** Decode one UTF-8 sequence, returning NULL if byte sequence is invalid.
  */
  static const char *utf8_decode (const char *o, int *val) {
    static const unsigned int limits[] = {0xFF, 0x7F, 0x7FF, 0xFFFF};
    const unsigned char *s = (const unsigned char *)o;
    unsigned int c = s[0];
    unsigned int res = 0;  /* final result */
    if (c < 0x80)  /* ascii? */
      res = c;
    else {
      int count = 0;  /* to count number of continuation bytes */
      while (c & 0x40) {  /* still have continuation bytes? */
        int cc = 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 */
        c <<= 1;  /* to test next bit */
      }
      res |= ((c & 0x7F) << (count * 5));  /* add first byte */
      if (count > 3 || res > MAXUNICODE || res <= limits[count])
        return NULL;  /* invalid byte sequence */
      s += count;  /* skip continuation bytes read */
    }
    if (val) *val = res;
    return (const char *)s + 1;  /* +1 to include first byte */
  }
  
  
  /*
  ** utf8len(s [, i [, j]]) --> number of characters that start in the
  ** range [i,j], or nil + current position if 's' is not well formed in
  ** that interval
  */
  static int utflen (lua_State *L) {
    int n = 0;
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer posi = u_posrelat(luaL_optinteger(L, 2, 1), len);
    lua_Integer posj = u_posrelat(luaL_optinteger(L, 3, -1), len);
    luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 2,
                     "initial position out of string");
    luaL_argcheck(L, --posj < (lua_Integer)len, 3,
                     "final position out of string");
    while (posi <= posj) {
      const char *s1 = utf8_decode(s + posi, NULL);
      if (s1 == NULL) {  /* conversion error? */
        lua_pushnil(L);  /* return nil ... */
        lua_pushinteger(L, posi + 1);  /* ... and current position */
        return 2;
      }
      posi = s1 - s;
      n++;
    }
    lua_pushinteger(L, n);
    return 1;
  }
  
  
  /*
  ** codepoint(s, [i, [j]])  -> returns codepoints for all characters
  ** that start in the range [i,j]
  */
  static int codepoint (lua_State *L) {
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer posi = u_posrelat(luaL_optinteger(L, 2, 1), len);
    lua_Integer pose = u_posrelat(luaL_optinteger(L, 3, posi), len);
    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;
    se = s + pose;
    for (s += posi - 1; s < se;) {
      int code;
      s = utf8_decode(s, &code);
      if (s == NULL)
        return luaL_error(L, "invalid UTF-8 code");
      lua_pushinteger(L, code);
      n++;
    }
    return n;
  }
  
  
  static void pushutfchar (lua_State *L, int arg) {
    lua_Integer code = luaL_checkinteger(L, arg);
    luaL_argcheck(L, 0 <= code && code <= MAXUNICODE, arg, "value out of range");
    lua_pushfstring(L, "%U", (long)code);
  }
  
  
  /*
  ** utfchar(n1, n2, ...)  -> char(n1)..char(n2)...
  */
  static int utfchar (lua_State *L) {
    int n = lua_gettop(L);  /* number of arguments */
    if (n == 1)  /* optimize common case of single char */
      pushutfchar(L, 1);
    else {
      int i;
      luaL_Buffer b;
      luaL_buffinit(L, &b);
      for (i = 1; i <= n; i++) {
        pushutfchar(L, i);
        luaL_addvalue(&b);
      }
      luaL_pushresult(&b);
    }
    return 1;
  }
  
  
  /*
  ** offset(s, n, [i])  -> index where n-th character counting from
  **   position 'i' starts; 0 means character at 'i'.
  */
  static int byteoffset (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 = u_posrelat(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 iter_aux (lua_State *L) {
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer n = lua_tointeger(L, 2) - 1;
    if (n < 0)  /* first iteration? */
      n = 0;  /* start from here */
    else if (n < (lua_Integer)len) {
      n++;  /* skip current byte */
      while (iscont(s + n)) n++;  /* and its continuations */
    }
    if (n >= (lua_Integer)len)
      return 0;  /* no more codepoints */
    else {
      int code;
      const char *next = utf8_decode(s + n, &code);
      if (next == NULL || iscont(next))
        return luaL_error(L, "invalid UTF-8 code");
      lua_pushinteger(L, n + 1);
      lua_pushinteger(L, code);
      return 2;
    }
  }
  
  
  static int iter_codes (lua_State *L) {
    luaL_checkstring(L, 1);
    lua_pushcfunction(L, iter_aux);
    lua_pushvalue(L, 1);
    lua_pushinteger(L, 0);
    return 3;
  }
  
  
  /* pattern to match a single UTF-8 character */
  #define UTF8PATT	"[\0-\x7F\xC2-\xF4][\x80-\xBF]*"
  
  
  static const luaL_Reg funcs[] = {
    {"offset", byteoffset},
    {"codepoint", codepoint},
    {"char", utfchar},
    {"len", utflen},
    {"codes", iter_codes},
    /* placeholders */
    {"charpattern", NULL},
    {NULL, NULL}
  };
  
  
  LUAMOD_API int luaopen_utf8 (lua_State *L) {
    luaL_newlib(L, funcs);
    lua_pushlstring(L, UTF8PATT, sizeof(UTF8PATT)/sizeof(char) - 1);
    lua_setfield(L, -2, "charpattern");
    return 1;
  }
  
  LUAMOD_API const luaL_Reg* luaexport_utf8_funcs()
  {
      return funcs;
  }
  
  
  