1 /* deflate_slow.c -- compress data using the slow strategy of deflation algorithm
2 *
3 * Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
4 * For conditions of distribution and use, see copyright notice in zlib.h
5 */
6
7 #include "zbuild.h"
8 #include "deflate.h"
9 #include "deflate_p.h"
10 #include "functable.h"
11
12 /* ===========================================================================
13 * Same as deflate_medium, but achieves better compression. We use a lazy
14 * evaluation for matches: a match is finally adopted only if there is
15 * no better match at the next window position.
16 */
deflate_slow(deflate_state * s,int flush)17 Z_INTERNAL block_state deflate_slow(deflate_state *s, int flush) {
18 Pos hash_head; /* head of hash chain */
19 int bflush; /* set if current block must be flushed */
20 uint32_t match_len;
21
22 /* Process the input block. */
23 for (;;) {
24 /* Make sure that we always have enough lookahead, except
25 * at the end of the input file. We need MAX_MATCH bytes
26 * for the next match, plus MIN_MATCH bytes to insert the
27 * string following the next match.
28 */
29 if (s->lookahead < MIN_LOOKAHEAD) {
30 fill_window(s);
31 if (UNLIKELY(s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH)) {
32 return need_more;
33 }
34 if (UNLIKELY(s->lookahead == 0))
35 break; /* flush the current block */
36 }
37
38 /* Insert the string window[strstart .. strstart+2] in the
39 * dictionary, and set hash_head to the head of the hash chain:
40 */
41 hash_head = NIL;
42 if (LIKELY(s->lookahead >= MIN_MATCH)) {
43 hash_head = functable.quick_insert_string(s, s->strstart);
44 }
45
46 /* Find the longest match, discarding those <= prev_length.
47 */
48 s->prev_match = (Pos)s->match_start;
49 match_len = MIN_MATCH-1;
50
51 if (hash_head != NIL && s->prev_length < s->max_lazy_match && s->strstart - hash_head <= MAX_DIST(s)) {
52 /* To simplify the code, we prevent matches with the string
53 * of window index 0 (in particular we have to avoid a match
54 * of the string with itself at the start of the input file).
55 */
56 match_len = functable.longest_match(s, hash_head);
57 /* longest_match() sets match_start */
58
59 if (match_len <= 5 && (s->strategy == Z_FILTERED)) {
60 /* If prev_match is also MIN_MATCH, match_start is garbage
61 * but we will ignore the current match anyway.
62 */
63 match_len = MIN_MATCH-1;
64 }
65 }
66 /* If there was a match at the previous step and the current
67 * match is not better, output the previous match:
68 */
69 if (s->prev_length >= MIN_MATCH && match_len <= s->prev_length) {
70 unsigned int max_insert = s->strstart + s->lookahead - MIN_MATCH;
71 /* Do not insert strings in hash table beyond this. */
72
73 check_match(s, s->strstart-1, s->prev_match, s->prev_length);
74
75 bflush = zng_tr_tally_dist(s, s->strstart -1 - s->prev_match, s->prev_length - MIN_MATCH);
76
77 /* Insert in hash table all strings up to the end of the match.
78 * strstart-1 and strstart are already inserted. If there is not
79 * enough lookahead, the last two strings are not inserted in
80 * the hash table.
81 */
82 s->lookahead -= s->prev_length-1;
83
84 unsigned int mov_fwd = s->prev_length - 2;
85 if (max_insert > s->strstart) {
86 unsigned int insert_cnt = mov_fwd;
87 if (UNLIKELY(insert_cnt > max_insert - s->strstart))
88 insert_cnt = max_insert - s->strstart;
89
90 functable.insert_string(s, s->strstart + 1, insert_cnt);
91 }
92 s->prev_length = 0;
93 s->match_available = 0;
94 s->strstart += mov_fwd + 1;
95
96 if (UNLIKELY(bflush))
97 FLUSH_BLOCK(s, 0);
98
99 } else if (s->match_available) {
100 /* If there was no match at the previous position, output a
101 * single literal. If there was a match but the current match
102 * is longer, truncate the previous match to a single literal.
103 */
104 bflush = zng_tr_tally_lit(s, s->window[s->strstart-1]);
105 if (UNLIKELY(bflush))
106 FLUSH_BLOCK_ONLY(s, 0);
107 s->prev_length = match_len;
108 s->strstart++;
109 s->lookahead--;
110 if (UNLIKELY(s->strm->avail_out == 0))
111 return need_more;
112 } else {
113 /* There is no previous match to compare with, wait for
114 * the next step to decide.
115 */
116 s->prev_length = match_len;
117 s->match_available = 1;
118 s->strstart++;
119 s->lookahead--;
120 }
121 }
122 Assert(flush != Z_NO_FLUSH, "no flush?");
123 if (UNLIKELY(s->match_available)) {
124 (void) zng_tr_tally_lit(s, s->window[s->strstart-1]);
125 s->match_available = 0;
126 }
127 s->insert = s->strstart < MIN_MATCH-1 ? s->strstart : MIN_MATCH-1;
128 if (UNLIKELY(flush == Z_FINISH)) {
129 FLUSH_BLOCK(s, 1);
130 return finish_done;
131 }
132 if (UNLIKELY(s->sym_next))
133 FLUSH_BLOCK(s, 0);
134 return block_done;
135 }
136