if (lookahead >= MIN_MATCH) {
                    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);