#define US4B  0x80, 0xBF /* for lead bytes 0xF1-0xF3 */
#define US4C  0x80, 0x8F /* for lead byte 0xF4 */
#define US0A  0xFF, 0x00 /* for any other lead byte */

/* a table used for quick lookup of the definition that goes with a
 * particular lead byte */
static const unsigned char lb_tab[] = {
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US0A, US0A, US0A, US0A, US0A, US0A, US0A, US0A,
  US2A, US0A, US2B, US2B, US2B, US2B, US2B, US2B,
  US2B, US2B, US2B, US2B, US2B, US2B, US2B, US2B,
  US2B, US2B, US2B, US2B, US2B, US2B, US2B, US2B,
  US2B, US2B, US2B, US2B, US2B, US2B, US2B, US2B,
  US3A, US3B, US3B, US3B, US3B, US3B, US3B, US3B,
  US3B, US3B, US3B, US3B, US3B, US3B, US3B, US3B,
  US4A, US4B, US4B, US4B, US4C, US0A, US0A, US0A,

  unsigned char c, c2;

  if( n==0 ) return 0;  /* Empty file -> OK */
  c = *z;
  while( --n>0 ){
    c2 = c;
    c = *++z;
    if( c2>=0x80 ){
      const unsigned char *def = &lb_tab[(2*c2)-0x100];
      if( (c<*def) || (c>*++def) ){
        return LOOK_INVALID; /* Invalid UTF-8 */
      }
      if( c2>=0xe0 ){
        c = (c2<<1)|3;
      }else{
        c = ' ';
      }


    }
  }
  return (c>=0x80) ? LOOK_INVALID : 0; /* Last byte must be ASCII. */
}

/*
** Define the type needed to represent a Unicode (UTF-16) character.