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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
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 }