1 ///////////////////////////////////////////////////////////////////////////////
2 //
3 /// \file lzma_encoder_optimum_fast.c
4 //
5 // Author: Igor Pavlov
6 //
7 // This file has been put into the public domain.
8 // You can do whatever you want with this file.
9 //
10 ///////////////////////////////////////////////////////////////////////////////
11
12 #include "lzma_encoder_private.h"
13 #include "memcmplen.h"
14
15
16 #define change_pair(small_dist, big_dist) \
17 (((big_dist) >> 7) > (small_dist))
18
19
20 extern void
lzma_lzma_optimum_fast(lzma_coder * restrict coder,lzma_mf * restrict mf,uint32_t * restrict back_res,uint32_t * restrict len_res)21 lzma_lzma_optimum_fast(lzma_coder *restrict coder, lzma_mf *restrict mf,
22 uint32_t *restrict back_res, uint32_t *restrict len_res)
23 {
24 const uint32_t nice_len = mf->nice_len;
25
26 uint32_t len_main;
27 uint32_t matches_count;
28 if (mf->read_ahead == 0) {
29 len_main = mf_find(mf, &matches_count, coder->matches);
30 } else {
31 assert(mf->read_ahead == 1);
32 len_main = coder->longest_match_length;
33 matches_count = coder->matches_count;
34 }
35
36 const uint8_t *buf = mf_ptr(mf) - 1;
37 const uint32_t buf_avail = my_min(mf_avail(mf) + 1, MATCH_LEN_MAX);
38
39 if (buf_avail < 2) {
40 // There's not enough input left to encode a match.
41 *back_res = UINT32_MAX;
42 *len_res = 1;
43 return;
44 }
45
46 // Look for repeated matches; scan the previous four match distances
47 uint32_t rep_len = 0;
48 uint32_t rep_index = 0;
49
50 for (uint32_t i = 0; i < REPS; ++i) {
51 // Pointer to the beginning of the match candidate
52 const uint8_t *const buf_back = buf - coder->reps[i] - 1;
53
54 // If the first two bytes (2 == MATCH_LEN_MIN) do not match,
55 // this rep is not useful.
56 if (not_equal_16(buf, buf_back))
57 continue;
58
59 // The first two bytes matched.
60 // Calculate the length of the match.
61 const uint32_t len = lzma_memcmplen(
62 buf, buf_back, 2, buf_avail);
63
64 // If we have found a repeated match that is at least
65 // nice_len long, return it immediately.
66 if (len >= nice_len) {
67 *back_res = i;
68 *len_res = len;
69 mf_skip(mf, len - 1);
70 return;
71 }
72
73 if (len > rep_len) {
74 rep_index = i;
75 rep_len = len;
76 }
77 }
78
79 // We didn't find a long enough repeated match. Encode it as a normal
80 // match if the match length is at least nice_len.
81 if (len_main >= nice_len) {
82 *back_res = coder->matches[matches_count - 1].dist + REPS;
83 *len_res = len_main;
84 mf_skip(mf, len_main - 1);
85 return;
86 }
87
88 uint32_t back_main = 0;
89 if (len_main >= 2) {
90 back_main = coder->matches[matches_count - 1].dist;
91
92 while (matches_count > 1 && len_main ==
93 coder->matches[matches_count - 2].len + 1) {
94 if (!change_pair(coder->matches[
95 matches_count - 2].dist,
96 back_main))
97 break;
98
99 --matches_count;
100 len_main = coder->matches[matches_count - 1].len;
101 back_main = coder->matches[matches_count - 1].dist;
102 }
103
104 if (len_main == 2 && back_main >= 0x80)
105 len_main = 1;
106 }
107
108 if (rep_len >= 2) {
109 if (rep_len + 1 >= len_main
110 || (rep_len + 2 >= len_main
111 && back_main > (UINT32_C(1) << 9))
112 || (rep_len + 3 >= len_main
113 && back_main > (UINT32_C(1) << 15))) {
114 *back_res = rep_index;
115 *len_res = rep_len;
116 mf_skip(mf, rep_len - 1);
117 return;
118 }
119 }
120
121 if (len_main < 2 || buf_avail <= 2) {
122 *back_res = UINT32_MAX;
123 *len_res = 1;
124 return;
125 }
126
127 // Get the matches for the next byte. If we find a better match,
128 // the current byte is encoded as a literal.
129 coder->longest_match_length = mf_find(mf,
130 &coder->matches_count, coder->matches);
131
132 if (coder->longest_match_length >= 2) {
133 const uint32_t new_dist = coder->matches[
134 coder->matches_count - 1].dist;
135
136 if ((coder->longest_match_length >= len_main
137 && new_dist < back_main)
138 || (coder->longest_match_length == len_main + 1
139 && !change_pair(back_main, new_dist))
140 || (coder->longest_match_length > len_main + 1)
141 || (coder->longest_match_length + 1 >= len_main
142 && len_main >= 3
143 && change_pair(new_dist, back_main))) {
144 *back_res = UINT32_MAX;
145 *len_res = 1;
146 return;
147 }
148 }
149
150 // In contrast to LZMA SDK, dictionary could not have been moved
151 // between mf_find() calls, thus it is safe to just increment
152 // the old buf pointer instead of recalculating it with mf_ptr().
153 ++buf;
154
155 const uint32_t limit = my_max(2, len_main - 1);
156
157 for (uint32_t i = 0; i < REPS; ++i) {
158 if (memcmp(buf, buf - coder->reps[i] - 1, limit) == 0) {
159 *back_res = UINT32_MAX;
160 *len_res = 1;
161 return;
162 }
163 }
164
165 *back_res = back_main + REPS;
166 *len_res = len_main;
167 mf_skip(mf, len_main - 2);
168 return;
169 }
170