if (++strstart <= max_insert) {
                            ins_h = (((ins_h) << hash_shift) ^ (window[(strstart) + (MIN_MATCH - 1)] & 0xff)) & hash_mask;
                            // prev[strstart&w_mask]=hash_head=head[ins_h];
                            hash_head = (head[ins_h] & 0xffff);
                            prev[strstart & w_mask] = head[ins_h];