MAXXLEN
if (xlen > MAXXLEN)
xlen = MAXXLEN;
if ((len = xlen - MAXXLEN) <= 0)
xoff = offsetXAD(xad) + MAXXLEN;
xaddr = addressXAD(xad) + MAXXLEN;
xlen = MAXXLEN;
(lxlen + nxlen < MAXXLEN)) {
(rxlen + nxlen < MAXXLEN)) {