System.util.zlib.Deflate.deflate_slow C# (CSharp) Method

        internal int deflate_slow(int flush){
            //    short hash_head = 0;    // head of hash chain
            int hash_head = 0;    // head of hash chain
            bool bflush;         // set if current block must be flushed

            // Process the input block.
            while(true){
                // Make sure that we always have enough lookahead, except
                // at the end of the input file. We need MAX_MATCH bytes
                // for the next match, plus MIN_MATCH bytes to insert the
                // string following the next match.

                if (lookahead < MIN_LOOKAHEAD) {
                    fill_window();
                    if(lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) {
                        return NeedMore;
                    }
                    if(lookahead == 0) break; // flush the current block
                }

                // Insert the string window[strstart .. strstart+2] in the
                // dictionary, and set hash_head to the head of the hash chain:

                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);
                    prev[strstart&w_mask]=head[ins_h];
                    head[ins_h]=(short)strstart;
                }

                // Find the longest match, discarding those <= prev_length.
                prev_length = match_length; prev_match = match_start;
                match_length = MIN_MATCH-1;

                if (hash_head != 0 && prev_length < max_lazy_match &&
                    ((strstart-hash_head)&0xffff) <= w_size-MIN_LOOKAHEAD
                    ){
                    // To simplify the code, we prevent matches with the string
                    // of window index 0 (in particular we have to avoid a match
                    // of the string with itself at the start of the input file).

                    if(strategy != Z_HUFFMAN_ONLY) {
                        match_length = longest_match(hash_head);
                    }
                    // longest_match() sets match_start

                    if (match_length <= 5 && (strategy == Z_FILTERED ||
                        (match_length == MIN_MATCH &&
                        strstart - match_start > 4096))) {

                        // If prev_match is also MIN_MATCH, match_start is garbage
                        // but we will ignore the current match anyway.
                        match_length = MIN_MATCH-1;
                    }
                }

                // If there was a match at the previous step and the current
                // match is not better, output the previous match:
                if(prev_length >= MIN_MATCH && match_length <= prev_length) {
                    int max_insert = strstart + lookahead - MIN_MATCH;
                    // Do not insert strings in hash table beyond this.

                    //          check_match(strstart-1, prev_match, prev_length);

                    bflush=_tr_tally(strstart-1-prev_match, prev_length - MIN_MATCH);

                    // Insert in hash table all strings up to the end of the match.
                    // strstart-1 and strstart are already inserted. If there is not
                    // enough lookahead, the last two strings are not inserted in
                    // the hash table.
                    lookahead -= prev_length-1;
                    prev_length -= 2;
                    do{
                        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];
                            head[ins_h]=(short)strstart;
                        }
                    }
                    while(--prev_length != 0);
                    match_available = 0;
                    match_length = MIN_MATCH-1;
                    strstart++;

                    if (bflush){
                        flush_block_only(false);
                        if(strm.avail_out==0) return NeedMore;
                    }
                } else if (match_available!=0) {

                    // If there was no match at the previous position, output a
                    // single literal. If there was a match but the current match
                    // is longer, truncate the previous match to a single literal.

                    bflush=_tr_tally(0, window[strstart-1]&0xff);

                    if (bflush) {
                        flush_block_only(false);
                    }
                    strstart++;
                    lookahead--;
                    if(strm.avail_out == 0) return NeedMore;
                } else {
                    // There is no previous match to compare with, wait for
                    // the next step to decide.

                    match_available = 1;
                    strstart++;
                    lookahead--;
                }
            }

            if(match_available!=0) {
                bflush=_tr_tally(0, window[strstart-1]&0xff);
                match_available = 0;
            }
            flush_block_only(flush == Z_FINISH);

            if(strm.avail_out==0){
                if(flush == Z_FINISH) return FinishStarted;
                else return NeedMore;
            }

            return flush == Z_FINISH ? FinishDone : BlockDone;
        }