getth_off
thlen = (hlen + getth_off(th)) << 2;
getth_off(th) != getth_off(oth) ||
(getth_off(th) > 5 &&
BCMP(th + 1, oth + 1, (getth_off(th) - 5) << 2))) {
(hlen += getth_off(buf+hlen) << 2) > buflen || hlen > MAX_HDR) {