1 /* deflate_fast.c -- compress data using the fast 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 * Compress as much as possible from the input stream, return the current
14 * block state.
15 * This function does not perform lazy evaluation of matches and inserts
16 * new strings in the dictionary only for unmatched strings or for short
17 * matches. It is used only for the fast compression options.
18 */
deflate_fast(deflate_state * s,int flush)19 Z_INTERNAL block_state deflate_fast(deflate_state *s, int flush) {
20 Pos hash_head; /* head of the hash chain */
21 int bflush = 0; /* set if current block must be flushed */
22 uint32_t match_len = 0;
23
24 for (;;) {
25 /* Make sure that we always have enough lookahead, except
26 * at the end of the input file. We need MAX_MATCH bytes
27 * for the next match, plus MIN_MATCH bytes to insert the
28 * string following the next match.
29 */
30 if (s->lookahead < MIN_LOOKAHEAD) {
31 fill_window(s);
32 if (UNLIKELY(s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH)) {
33 return need_more;
34 }
35 if (UNLIKELY(s->lookahead == 0))
36 break; /* flush the current block */
37 }
38
39 /* Insert the string window[strstart .. strstart+2] in the
40 * dictionary, and set hash_head to the head of the hash chain:
41 */
42 if (s->lookahead >= MIN_MATCH) {
43 hash_head = functable.quick_insert_string(s, s->strstart);
44 /* Find the longest match, discarding those <= prev_length.
45 * At this point we have always match length < MIN_MATCH
46 */
47 if (hash_head != 0 && s->strstart - hash_head <= MAX_DIST(s)) {
48 /* To simplify the code, we prevent matches with the string
49 * of window index 0 (in particular we have to avoid a match
50 * of the string with itself at the start of the input file).
51 */
52 match_len = functable.longest_match(s, hash_head);
53 /* longest_match() sets match_start */
54 }
55 }
56
57 if (match_len >= MIN_MATCH) {
58 check_match(s, s->strstart, s->match_start, match_len);
59
60 bflush = zng_tr_tally_dist(s, s->strstart - s->match_start, match_len - MIN_MATCH);
61
62 s->lookahead -= match_len;
63
64 /* Insert new strings in the hash table only if the match length
65 * is not too large. This saves time but degrades compression.
66 */
67 if (match_len <= s->max_insert_length && s->lookahead >= MIN_MATCH) {
68 match_len--; /* string at strstart already in table */
69 s->strstart++;
70
71 functable.insert_string(s, s->strstart, match_len);
72 s->strstart += match_len;
73 } else {
74 s->strstart += match_len;
75 #if MIN_MATCH != 3
76 functable.insert_string(s, s->strstart + 2 - MIN_MATCH, MIN_MATCH - 2);
77 #else
78 functable.quick_insert_string(s, s->strstart + 2 - MIN_MATCH);
79 #endif
80 /* If lookahead < MIN_MATCH, ins_h is garbage, but it does not
81 * matter since it will be recomputed at next deflate call.
82 */
83 }
84 match_len = 0;
85 } else {
86 /* No match, output a literal byte */
87 bflush = zng_tr_tally_lit(s, s->window[s->strstart]);
88 s->lookahead--;
89 s->strstart++;
90 }
91 if (UNLIKELY(bflush))
92 FLUSH_BLOCK(s, 0);
93 }
94 s->insert = s->strstart < MIN_MATCH-1 ? s->strstart : MIN_MATCH-1;
95 if (UNLIKELY(flush == Z_FINISH)) {
96 FLUSH_BLOCK(s, 1);
97 return finish_done;
98 }
99 if (UNLIKELY(s->sym_next))
100 FLUSH_BLOCK(s, 0);
101 return block_done;
102 }
103