HMASK
return(((hv >> 16) ^ hv) & HMASK);
ip->hnext = hist_hash[ip->hv & HMASK];
hist_hash[ip->hv & HMASK] = ip;
for (scan = hist_hash[ip->hv & HMASK]; scan; scan = scan->hnext) {
scanp = &hist_hash[ip->hv & HMASK];