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 #define FAST_ONE_PASS_COMPRESSION_QUALITY 0
16 #define FAST_TWO_PASS_COMPRESSION_QUALITY 1
17 #define ZOPFLIFICATION_QUALITY 10
18 #define HQ_ZOPFLIFICATION_QUALITY 11
19
20 #define MAX_QUALITY_FOR_STATIC_ENTROPY_CODES 2
21 #define MIN_QUALITY_FOR_BLOCK_SPLIT 4
22 #define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4
23 #define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5
24 #define MIN_QUALITY_FOR_CONTEXT_MODELING 5
25 #define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7
26 #define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10
27 /* Only for "font" mode. */
28 #define MIN_QUALITY_FOR_RECOMPUTE_DISTANCE_PREFIXES 10
29
30 /* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
31 so we buffer at most this much literals and commands. */
32 #define MAX_NUM_DELAYED_SYMBOLS 0x2fff
33
34 typedef struct BrotliHasherParams {
35 int type;
36 int bucket_bits;
37 int block_bits;
38 int hash_len;
39 int num_last_distances_to_check;
40 } BrotliHasherParams;
41
42 /* Encoding parameters */
43 typedef struct BrotliEncoderParams {
44 BrotliEncoderMode mode;
45 int quality;
46 int lgwin;
47 int lgblock;
48 size_t size_hint;
49 BROTLI_BOOL disable_literal_context_modeling;
50 BrotliHasherParams hasher;
51 } BrotliEncoderParams;
52
53 /* Returns hash-table size for quality levels 0 and 1. */
MaxHashTableSize(int quality)54 static BROTLI_INLINE size_t MaxHashTableSize(int quality) {
55 return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17;
56 }
57
58 /* The maximum length for which the zopflification uses distinct distances. */
59 #define MAX_ZOPFLI_LEN_QUALITY_10 150
60 #define MAX_ZOPFLI_LEN_QUALITY_11 325
61
62 /* Do not thoroughly search when a long copy is found. */
63 #define BROTLI_LONG_COPY_QUICK_STEP 16384
64
MaxZopfliLen(const BrotliEncoderParams * params)65 static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) {
66 return params->quality <= 10 ?
67 MAX_ZOPFLI_LEN_QUALITY_10 :
68 MAX_ZOPFLI_LEN_QUALITY_11;
69 }
70
71 /* Number of best candidates to evaluate to expand Zopfli chain. */
MaxZopfliCandidates(const BrotliEncoderParams * params)72 static BROTLI_INLINE size_t MaxZopfliCandidates(
73 const BrotliEncoderParams* params) {
74 return params->quality <= 10 ? 1 : 5;
75 }
76
SanitizeParams(BrotliEncoderParams * params)77 static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) {
78 params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY,
79 BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality));
80 if (params->lgwin < BROTLI_MIN_WINDOW_BITS) {
81 params->lgwin = BROTLI_MIN_WINDOW_BITS;
82 } else if (params->lgwin > BROTLI_MAX_WINDOW_BITS) {
83 params->lgwin = BROTLI_MAX_WINDOW_BITS;
84 }
85 }
86
87 /* Returns optimized lg_block value. */
ComputeLgBlock(const BrotliEncoderParams * params)88 static BROTLI_INLINE int ComputeLgBlock(const BrotliEncoderParams* params) {
89 int lgblock = params->lgblock;
90 if (params->quality == FAST_ONE_PASS_COMPRESSION_QUALITY ||
91 params->quality == FAST_TWO_PASS_COMPRESSION_QUALITY) {
92 lgblock = params->lgwin;
93 } else if (params->quality < MIN_QUALITY_FOR_BLOCK_SPLIT) {
94 lgblock = 14;
95 } else if (lgblock == 0) {
96 lgblock = 16;
97 if (params->quality >= 9 && params->lgwin > lgblock) {
98 lgblock = BROTLI_MIN(int, 18, params->lgwin);
99 }
100 } else {
101 lgblock = BROTLI_MIN(int, BROTLI_MAX_INPUT_BLOCK_BITS,
102 BROTLI_MAX(int, BROTLI_MIN_INPUT_BLOCK_BITS, lgblock));
103 }
104 return lgblock;
105 }
106
107 /* Returns log2 of the size of main ring buffer area.
108 Allocate at least lgwin + 1 bits for the ring buffer so that the newly
109 added block fits there completely and we still get lgwin bits and at least
110 read_block_size_bits + 1 bits because the copy tail length needs to be
111 smaller than ring-buffer size. */
ComputeRbBits(const BrotliEncoderParams * params)112 static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
113 return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
114 }
115
MaxMetablockSize(const BrotliEncoderParams * params)116 static BROTLI_INLINE size_t MaxMetablockSize(
117 const BrotliEncoderParams* params) {
118 int bits =
119 BROTLI_MIN(int, ComputeRbBits(params), BROTLI_MAX_INPUT_BLOCK_BITS);
120 return (size_t)1 << bits;
121 }
122
123 /* When searching for backward references and have not seen matches for a long
124 time, we can skip some match lookups. Unsuccessful match lookups are very
125 expensive and this kind of a heuristic speeds up compression quite a lot.
126 At first 8 byte strides are taken and every second byte is put to hasher.
127 After 4x more literals stride by 16 bytes, every put 4-th byte to hasher.
128 Applied only to qualities 2 to 9. */
LiteralSpreeLengthForSparseSearch(const BrotliEncoderParams * params)129 static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
130 const BrotliEncoderParams* params) {
131 return params->quality < 9 ? 64 : 512;
132 }
133
ChooseHasher(const BrotliEncoderParams * params,BrotliHasherParams * hparams)134 static BROTLI_INLINE void ChooseHasher(const BrotliEncoderParams* params,
135 BrotliHasherParams* hparams) {
136 if (params->quality > 9) {
137 hparams->type = 10;
138 } else if (params->quality == 4 && params->size_hint >= (1 << 20)) {
139 hparams->type = 54;
140 } else if (params->quality < 5) {
141 hparams->type = params->quality;
142 } else if (params->lgwin <= 16) {
143 hparams->type = params->quality < 7 ? 40 : params->quality < 9 ? 41 : 42;
144 } else if (params->size_hint >= (1 << 20) && params->lgwin >= 19) {
145 hparams->type = 6;
146 hparams->block_bits = params->quality - 1;
147 hparams->bucket_bits = 15;
148 hparams->hash_len = 5;
149 hparams->num_last_distances_to_check =
150 params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
151 } else {
152 hparams->type = 5;
153 hparams->block_bits = params->quality - 1;
154 hparams->bucket_bits = params->quality < 7 ? 14 : 15;
155 hparams->num_last_distances_to_check =
156 params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
157 }
158 }
159
160 #endif /* BROTLI_ENC_QUALITY_H_ */
161