text: /*
  ** $Id: lutf8lib.c,v 1.16 2016/12/22 13:08:50 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))
              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;
  }
  
  