regex.c:491
static unsigned int
utf8_firstbyte(c)
     unsigned long c;
{
  if (c < 0x80) return c;
  if (c <= 0x7ff) return ((c>>6)&0xff)|0xc0;
  if (c <= 0xffff) return ((c>>12)&0xff)|0xe0;
  if (c <= 0x1fffff) return ((c>>18)&0xff)|0xf0;
  if (c <= 0x3ffffff) return ((c>>24)&0xff)|0xf8;
  if (c <= 0x7fffffff) return ((c>>30)&0xff)|0xfc;
#if SIZEOF_INT > 4
  if (c <= 0xfffffffff) return 0xfe;
#else
  return 0xfe;
#endif
}
