text: /* deflate_slow.c -- compress data using the slow strategy of deflation algorithm
   *
   * Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
   * For conditions of distribution and use, see copyright notice in zlib.h
   */
  
  #include "zbuild.h"
  #include "deflate.h"
  #include "deflate_p.h"
  #include "functable.h"
  
  /* ===========================================================================
   * Same as deflate_medium, but achieves better compression. We use a lazy
   * evaluation for matches: a match is finally adopted only if there is
   * no better match at the next window position.
   */
  ZLIB_INTERNAL block_state deflate_slow(deflate_state *s, int flush) {
      Pos hash_head;           /* head of hash chain */
      int bflush;              /* set if current block must be flushed */
      uint32_t match_len;
  
      /* Process the input block. */
      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 (UNLIKELY(s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH)) {
                  return need_more;
              }
              if (UNLIKELY(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 = NIL;
          if (LIKELY(s->lookahead >= MIN_MATCH)) {
              hash_head = functable.quick_insert_string(s, s->strstart);
          }
  
          /* Find the longest match, discarding those <= prev_length.
           */
          s->prev_match = s->match_start;
          match_len = MIN_MATCH-1;
  
          if (hash_head != NIL && s->prev_length < s->max_lazy_match && s->strstart - hash_head <= MAX_DIST(s)) {
              /* 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).
               */
              match_len = functable.longest_match(s, hash_head);
              /* longest_match() sets match_start */
  
              if (match_len <= 5 && (s->strategy == Z_FILTERED)) {
                  /* If prev_match is also MIN_MATCH, match_start is garbage
                   * but we will ignore the current match anyway.
                   */
                  match_len = MIN_MATCH-1;
              }
          }
          /* If there was a match at the previous step and the current
           * match is not better, output the previous match:
           */
          if (s->prev_length >= MIN_MATCH && match_len <= s->prev_length) {
              unsigned int max_insert = s->strstart + s->lookahead - MIN_MATCH;
              /* Do not insert strings in hash table beyond this. */
  
              check_match(s, s->strstart-1, s->prev_match, s->prev_length);
  
              bflush = zng_tr_tally_dist(s, s->strstart -1 - s->prev_match, s->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.
               */
              s->lookahead -= s->prev_length-1;
  
              unsigned int mov_fwd = s->prev_length - 2;
              if (max_insert > s->strstart) {
                  unsigned int insert_cnt = mov_fwd;
                  if (UNLIKELY(insert_cnt > max_insert - s->strstart))
                      insert_cnt = max_insert - s->strstart;
  
                  functable.insert_string(s, s->strstart + 1, insert_cnt);
              }
              s->prev_length = 0;
              s->match_available = 0;
              s->strstart += mov_fwd + 1;
  
              if (UNLIKELY(bflush))
                  FLUSH_BLOCK(s, 0);
  
          } else if (s->match_available) {
              /* 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 = zng_tr_tally_lit(s, s->window[s->strstart-1]);
              if (UNLIKELY(bflush))
                  FLUSH_BLOCK_ONLY(s, 0);
              s->prev_length = match_len;
              s->strstart++;
              s->lookahead--;
              if (UNLIKELY(s->strm->avail_out == 0))
                  return need_more;
          } else {
              /* There is no previous match to compare with, wait for
               * the next step to decide.
               */
              s->prev_length = match_len;
              s->match_available = 1;
              s->strstart++;
              s->lookahead--;
          }
      }
      Assert(flush != Z_NO_FLUSH, "no flush?");
      if (UNLIKELY(s->match_available)) {
          (void) zng_tr_tally_lit(s, s->window[s->strstart-1]);
          s->match_available = 0;
      }
      s->insert = s->strstart < MIN_MATCH-1 ? s->strstart : MIN_MATCH-1;
      if (UNLIKELY(flush == Z_FINISH)) {
          FLUSH_BLOCK(s, 1);
          return finish_done;
      }
      if (UNLIKELY(s->sym_next))
          FLUSH_BLOCK(s, 0);
      return block_done;
  }
  