Function deflate_fast

Picviewer CE+/dist.user.js:6731–6852

(s, flush)

 * matches. It is used only for the fast compression options.
 */
function deflate_fast(s, flush) {
  var hash_head;        /* head of the hash chain */
  var bflush;           /* set if current block must be flushed */

  for (;;) {
    /* 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 (s.lookahead < MIN_LOOKAHEAD) {
      fill_window(s);
      if (s.lookahead < MIN_LOOKAHEAD && flush === Z_NO_FLUSH) {
        return BS_NEED_MORE;
      }
      if (s.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:
     */
    hash_head = 0/*NIL*/;
    if (s.lookahead >= MIN_MATCH) {
      /*** INSERT_STRING(s, s.strstart, hash_head); ***/
      s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
      hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
      s.head[s.ins_h] = s.strstart;
      /***/
    }

    /* Find the longest match, discarding those <= prev_length.
     * At this point we have always match_length < MIN_MATCH
     */
    if (hash_head !== 0/*NIL*/ && ((s.strstart - hash_head) <= (s.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).
       */
      s.match_length = longest_match(s, hash_head);
      /* longest_match() sets match_start */
    }
    if (s.match_length >= MIN_MATCH) {
      // check_match(s, s.strstart, s.match_start, s.match_length); // for debug only

      /*** _tr_tally_dist(s, s.strstart - s.match_start,
                     s.match_length - MIN_MATCH, bflush); ***/
      bflush = trees._tr_tally(s, s.strstart - s.match_start, s.match_length - MIN_MATCH);

      s.lookahead -= s.match_length;

      /* Insert new strings in the hash table only if the match length
       * is not too large. This saves time but degrades compression.
       */
      if (s.match_length <= s.max_lazy_match/*max_insert_length*/ && s.lookahead >= MIN_MATCH) {
        s.match_length--; /* string at strstart already in table */
        do {