static void hex2bin(unsigned char *to, const char *p, size_t len) {
	register char c1, c2;

	for (; *p; to++) {
		c1 = *p++; c2 = *p++;
		if (!c1 || !isxdigit(c1))
			return;
		else if (!c2 || !isxdigit(c2))
			*to = (unsigned char) digittoint(c1);
		else
			*to = (unsigned char) (digittoint(c1) << 4) | digittoint(c2);
	}
}