Fossil

** Java and Tcl use it. This function also considers valid
** the derivatives CESU-8 & WTF-8 (as described in the same
** wikipedia article referenced previously).
*/

/* definitions for various UTF-8 sequence lengths */
static const unsigned char us2a[] = {
  2, 0xC0, 0xC0, 0x80, 0x80
};
static const unsigned char us2b[] = {
  2, 0xC2, 0xDF, 0x80, 0xBF
};
static const unsigned char us3a[] = {
  3, 0xE0, 0xE0, 0xA0, 0xBF, 0x80, 0xBF
};
static const unsigned char us3b[] = {
  3, 0xE1, 0xEF, 0x80, 0xBF, 0x80, 0xBF
};
static const unsigned char us4a[] = {
  4, 0xF0, 0xF0, 0x90, 0xBF, 0x80, 0xBF, 0x80, 0xBF
};
static const unsigned char us4b[] = {
  4, 0xF1, 0xF3, 0x80, 0xBF, 0x80, 0xBF, 0x80, 0xBF
};
static const unsigned char us4c[] = {
  4, 0xF4, 0xF4, 0x80, 0x8F, 0x80, 0xBF, 0x80, 0xBF
};

/* a table used for quick lookup of the definition that goes with a
 * particular lead byte */
static const unsigned char* lb_tab[] = {
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
  NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,

  while( n>0 ){
    /* ascii is trivial */
    if( *z<0x80 ){
      ++z;
      --n;
    }else{
      /* get the definition for this lead byte */
      unsigned char* def = lb_tab[(*z++)-0x80];
      unsigned char i, len;

      /* if the definition doesn't exist, return invalid */
      if( !def ) return LOOK_INVALID;
      /* get the expected sequence length */
      len = *def;
      /* if there aren't enough bytes left, return invalid */
      if( n<len ) return LOOK_INVALID;
      /* skip the length & lead byte range */
      def += 3;
      /* we already know byte #0 is good, so check the remaining bytes */
      for(i=1; i<len; ++i){
        /* if the byte is outside the allowed range for this definition,
         * return invalid */
        if( (*z<*def++) || (*z++>*def++) ){
          return LOOK_INVALID;
        }