1 /* Copyright 2016 Google Inc. All Rights Reserved.
2
3 Distributed under MIT license.
4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
5 */
6
7 /* Constants and formulas that affect speed-ratio trade-offs and thus define
8 quality levels. */
9
10 #ifndef BROTLI_ENC_QUALITY_H_
11 #define BROTLI_ENC_QUALITY_H_
12
13 #include <brotli/encode.h>
14
15 #include "../common/platform.h"
16 #include "params.h"
17
18 #define FAST_ONE_PASS_COMPRESSION_QUALITY 0
19 #define FAST_TWO_PASS_COMPRESSION_QUALITY 1
20 #define ZOPFLIFICATION_QUALITY 10
21 #define HQ_ZOPFLIFICATION_QUALITY 11
22
23 #define MAX_QUALITY_FOR_STATIC_ENTROPY_CODES 2
24 #define MIN_QUALITY_FOR_BLOCK_SPLIT 4
25 #define MIN_QUALITY_FOR_NONZERO_DISTANCE_PARAMS 4
26 #define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4
27 #define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5
28 #define MIN_QUALITY_FOR_CONTEXT_MODELING 5
29 #define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7
30 #define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10
31
32 /* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
33 so we buffer at most this much literals and commands. */
34 #define MAX_NUM_DELAYED_SYMBOLS 0x2FFF
35
36 /* Returns hash-table size for quality levels 0 and 1. */
MaxHashTableSize(int quality)37 static BROTLI_INLINE size_t MaxHashTableSize(int quality) {
38 return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17;
39 }
40
41 /* The maximum length for which the zopflification uses distinct distances. */
42 #define MAX_ZOPFLI_LEN_QUALITY_10 150
43 #define MAX_ZOPFLI_LEN_QUALITY_11 325
44
45 /* Do not thoroughly search when a long copy is found. */
46 #define BROTLI_LONG_COPY_QUICK_STEP 16384
47
MaxZopfliLen(const BrotliEncoderParams * params)48 static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) {
49 return params->quality <= 10 ?
50 MAX_ZOPFLI_LEN_QUALITY_10 :
51 MAX_ZOPFLI_LEN_QUALITY_11;
52 }
53
54 /* Number of best candidates to evaluate to expand Zopfli chain. */
MaxZopfliCandidates(const BrotliEncoderParams * params)55 static BROTLI_INLINE size_t MaxZopfliCandidates(
56 const BrotliEncoderParams* params) {
57 return params->quality <= 10 ? 1 : 5;
58 }
59
SanitizeParams(BrotliEncoderParams * params)60 static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) {
61 params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY,
62 BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality));
63 if (params->quality <= MAX_QUALITY_FOR_STATIC_ENTROPY_CODES) {
64 params->large_window = BROTLI_FALSE;
65 }
66 if (params->lgwin < BROTLI_MIN_WINDOW_BITS) {
67 params->lgwin = BROTLI_MIN_WINDOW_BITS;
68 } else {
69 int max_lgwin = params->large_window ? BROTLI_LARGE_MAX_WINDOW_BITS :
70 BROTLI_MAX_WINDOW_BITS;
71 if (params->lgwin > max_lgwin) params->lgwin = max_lgwin;
72 }
73 }
74
75 /* Returns optimized lg_block value. */
ComputeLgBlock(const BrotliEncoderParams * params)76 static BROTLI_INLINE int ComputeLgBlock(const BrotliEncoderParams* params) {
77 int lgblock = params->lgblock;
78 if (params->quality == FAST_ONE_PASS_COMPRESSION_QUALITY ||
79 params->quality == FAST_TWO_PASS_COMPRESSION_QUALITY) {
80 lgblock = params->lgwin;
81 } else if (params->quality < MIN_QUALITY_FOR_BLOCK_SPLIT) {
82 lgblock = 14;
83 } else if (lgblock == 0) {
84 lgblock = 16;
85 if (params->quality >= 9 && params->lgwin > lgblock) {
86 lgblock = BROTLI_MIN(int, 18, params->lgwin);
87 }
88 } else {
89 lgblock = BROTLI_MIN(int, BROTLI_MAX_INPUT_BLOCK_BITS,
90 BROTLI_MAX(int, BROTLI_MIN_INPUT_BLOCK_BITS, lgblock));
91 }
92 return lgblock;
93 }
94
95 /* Returns log2 of the size of main ring buffer area.
96 Allocate at least lgwin + 1 bits for the ring buffer so that the newly
97 added block fits there completely and we still get lgwin bits and at least
98 read_block_size_bits + 1 bits because the copy tail length needs to be
99 smaller than ring-buffer size. */
ComputeRbBits(const BrotliEncoderParams * params)100 static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
101 return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
102 }
103
MaxMetablockSize(const BrotliEncoderParams * params)104 static BROTLI_INLINE size_t MaxMetablockSize(
105 const BrotliEncoderParams* params) {
106 int bits =
107 BROTLI_MIN(int, ComputeRbBits(params), BROTLI_MAX_INPUT_BLOCK_BITS);
108 return (size_t)1 << bits;
109 }
110
111 /* When searching for backward references and have not seen matches for a long
112 time, we can skip some match lookups. Unsuccessful match lookups are very
113 expensive and this kind of a heuristic speeds up compression quite a lot.
114 At first 8 byte strides are taken and every second byte is put to hasher.
115 After 4x more literals stride by 16 bytes, every put 4-th byte to hasher.
116 Applied only to qualities 2 to 9. */
LiteralSpreeLengthForSparseSearch(const BrotliEncoderParams * params)117 static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
118 const BrotliEncoderParams* params) {
119 return params->quality < 9 ? 64 : 512;
120 }
121
122 /* Quality to hasher mapping:
123
124 - q02: h02 (longest_match_quickly), b16, l5
125
126 - q03: h03 (longest_match_quickly), b17, l5
127
128 - q04: h04 (longest_match_quickly), b17, l5
129 - q04: h54 (longest_match_quickly), b20, l7 | for large files
130
131 - q05: h05 (longest_match ), b14, l4
132 - q05: h06 (longest_match64 ), b15, l5 | for large files
133 - q05: h40 (forgetful_chain ), b15, l4 | for small window
134
135 - q06: h05 (longest_match ), b14, l4
136 - q06: h06 (longest_match64 ), b15, l5 | for large files
137 - q06: h40 (forgetful_chain ), b15, l4 | for small window
138
139 - q07: h05 (longest_match ), b15, l4
140 - q07: h06 (longest_match64 ), b15, l5 | for large files
141 - q07: h41 (forgetful_chain ), b15, l4 | for small window
142
143 - q08: h05 (longest_match ), b15, l4
144 - q08: h06 (longest_match64 ), b15, l5 | for large files
145 - q08: h41 (forgetful_chain ), b15, l4 | for small window
146
147 - q09: h05 (longest_match ), b15, l4
148 - q09: h06 (longest_match64 ), b15, l5 | for large files
149 - q09: h42 (forgetful_chain ), b15, l4 | for small window
150
151 - q10: t10 (to_binary_tree ), b17, l128
152
153 - q11: t10 (to_binary_tree ), b17, l128
154
155 Where "q" is quality, "h" is hasher type, "b" is bucket bits,
156 "l" is source len. */
ChooseHasher(const BrotliEncoderParams * params,BrotliHasherParams * hparams)157 static BROTLI_INLINE void ChooseHasher(const BrotliEncoderParams* params,
158 BrotliHasherParams* hparams) {
159 if (params->quality > 9) {
160 hparams->type = 10;
161 } else if (params->quality == 4 && params->size_hint >= (1 << 20)) {
162 hparams->type = 54;
163 } else if (params->quality < 5) {
164 hparams->type = params->quality;
165 } else if (params->lgwin <= 16) {
166 hparams->type = params->quality < 7 ? 40 : params->quality < 9 ? 41 : 42;
167 } else if (params->size_hint >= (1 << 20) && params->lgwin >= 19) {
168 hparams->type = 6;
169 hparams->block_bits = params->quality - 1;
170 hparams->bucket_bits = 15;
171 hparams->num_last_distances_to_check =
172 params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
173 } else {
174 /* TODO(eustas): often previous setting (H6) is faster and denser; consider
175 adding an option to use it. */
176 hparams->type = 5;
177 hparams->block_bits = params->quality - 1;
178 hparams->bucket_bits = params->quality < 7 ? 14 : 15;
179 hparams->num_last_distances_to_check =
180 params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
181 }
182
183 if (params->lgwin > 24) {
184 /* Different hashers for large window brotli: not for qualities <= 2,
185 these are too fast for large window. Not for qualities >= 10: their
186 hasher already works well with large window. So the changes are:
187 H3 --> H35: for quality 3.
188 H54 --> H55: for quality 4 with size hint > 1MB
189 H6 --> H65: for qualities 5, 6, 7, 8, 9. */
190 if (hparams->type == 3) {
191 hparams->type = 35;
192 }
193 if (hparams->type == 54) {
194 hparams->type = 55;
195 }
196 if (hparams->type == 6) {
197 hparams->type = 65;
198 }
199 }
200 }
201
202 #endif /* BROTLI_ENC_QUALITY_H_ */
203