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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 "../common/platform.h"
14 #include <brotli/encode.h>
15 #include "./params.h"
16 
17 #define FAST_ONE_PASS_COMPRESSION_QUALITY 0
18 #define FAST_TWO_PASS_COMPRESSION_QUALITY 1
19 #define ZOPFLIFICATION_QUALITY 10
20 #define HQ_ZOPFLIFICATION_QUALITY 11
21 
22 #define MAX_QUALITY_FOR_STATIC_ENTROPY_CODES 2
23 #define MIN_QUALITY_FOR_BLOCK_SPLIT 4
24 #define MIN_QUALITY_FOR_NONZERO_DISTANCE_PARAMS 4
25 #define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4
26 #define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5
27 #define MIN_QUALITY_FOR_CONTEXT_MODELING 5
28 #define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7
29 #define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10
30 
31 /* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
32    so we buffer at most this much literals and commands. */
33 #define MAX_NUM_DELAYED_SYMBOLS 0x2FFF
34 
35 /* Returns hash-table size for quality levels 0 and 1. */
MaxHashTableSize(int quality)36 static BROTLI_INLINE size_t MaxHashTableSize(int quality) {
37   return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17;
38 }
39 
40 /* The maximum length for which the zopflification uses distinct distances. */
41 #define MAX_ZOPFLI_LEN_QUALITY_10 150
42 #define MAX_ZOPFLI_LEN_QUALITY_11 325
43 
44 /* Do not thoroughly search when a long copy is found. */
45 #define BROTLI_LONG_COPY_QUICK_STEP 16384
46 
MaxZopfliLen(const BrotliEncoderParams * params)47 static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) {
48   return params->quality <= 10 ?
49       MAX_ZOPFLI_LEN_QUALITY_10 :
50       MAX_ZOPFLI_LEN_QUALITY_11;
51 }
52 
53 /* Number of best candidates to evaluate to expand Zopfli chain. */
MaxZopfliCandidates(const BrotliEncoderParams * params)54 static BROTLI_INLINE size_t MaxZopfliCandidates(
55   const BrotliEncoderParams* params) {
56   return params->quality <= 10 ? 1 : 5;
57 }
58 
SanitizeParams(BrotliEncoderParams * params)59 static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) {
60   params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY,
61       BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality));
62   if (params->quality <= MAX_QUALITY_FOR_STATIC_ENTROPY_CODES) {
63     params->large_window = BROTLI_FALSE;
64   }
65   if (params->lgwin < BROTLI_MIN_WINDOW_BITS) {
66     params->lgwin = BROTLI_MIN_WINDOW_BITS;
67   } else {
68     int max_lgwin = params->large_window ? BROTLI_LARGE_MAX_WINDOW_BITS :
69                                            BROTLI_MAX_WINDOW_BITS;
70     if (params->lgwin > max_lgwin) params->lgwin = max_lgwin;
71   }
72 }
73 
74 /* Returns optimized lg_block value. */
ComputeLgBlock(const BrotliEncoderParams * params)75 static BROTLI_INLINE int ComputeLgBlock(const BrotliEncoderParams* params) {
76   int lgblock = params->lgblock;
77   if (params->quality == FAST_ONE_PASS_COMPRESSION_QUALITY ||
78       params->quality == FAST_TWO_PASS_COMPRESSION_QUALITY) {
79     lgblock = params->lgwin;
80   } else if (params->quality < MIN_QUALITY_FOR_BLOCK_SPLIT) {
81     lgblock = 14;
82   } else if (lgblock == 0) {
83     lgblock = 16;
84     if (params->quality >= 9 && params->lgwin > lgblock) {
85       lgblock = BROTLI_MIN(int, 18, params->lgwin);
86     }
87   } else {
88     lgblock = BROTLI_MIN(int, BROTLI_MAX_INPUT_BLOCK_BITS,
89         BROTLI_MAX(int, BROTLI_MIN_INPUT_BLOCK_BITS, lgblock));
90   }
91   return lgblock;
92 }
93 
94 /* Returns log2 of the size of main ring buffer area.
95    Allocate at least lgwin + 1 bits for the ring buffer so that the newly
96    added block fits there completely and we still get lgwin bits and at least
97    read_block_size_bits + 1 bits because the copy tail length needs to be
98    smaller than ring-buffer size. */
ComputeRbBits(const BrotliEncoderParams * params)99 static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
100   return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
101 }
102 
MaxMetablockSize(const BrotliEncoderParams * params)103 static BROTLI_INLINE size_t MaxMetablockSize(
104     const BrotliEncoderParams* params) {
105   int bits =
106       BROTLI_MIN(int, ComputeRbBits(params), BROTLI_MAX_INPUT_BLOCK_BITS);
107   return (size_t)1 << bits;
108 }
109 
110 /* When searching for backward references and have not seen matches for a long
111    time, we can skip some match lookups. Unsuccessful match lookups are very
112    expensive and this kind of a heuristic speeds up compression quite a lot.
113    At first 8 byte strides are taken and every second byte is put to hasher.
114    After 4x more literals stride by 16 bytes, every put 4-th byte to hasher.
115    Applied only to qualities 2 to 9. */
LiteralSpreeLengthForSparseSearch(const BrotliEncoderParams * params)116 static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
117     const BrotliEncoderParams* params) {
118   return params->quality < 9 ? 64 : 512;
119 }
120 
ChooseHasher(const BrotliEncoderParams * params,BrotliHasherParams * hparams)121 static BROTLI_INLINE void ChooseHasher(const BrotliEncoderParams* params,
122                                        BrotliHasherParams* hparams) {
123   if (params->quality > 9) {
124     hparams->type = 10;
125   } else if (params->quality == 4 && params->size_hint >= (1 << 20)) {
126     hparams->type = 54;
127   } else if (params->quality < 5) {
128     hparams->type = params->quality;
129   } else if (params->lgwin <= 16) {
130     hparams->type = params->quality < 7 ? 40 : params->quality < 9 ? 41 : 42;
131   } else if (params->size_hint >= (1 << 20) && params->lgwin >= 19) {
132     hparams->type = 6;
133     hparams->block_bits = params->quality - 1;
134     hparams->bucket_bits = 15;
135     hparams->hash_len = 5;
136     hparams->num_last_distances_to_check =
137         params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
138   } else {
139     hparams->type = 5;
140     hparams->block_bits = params->quality - 1;
141     hparams->bucket_bits = params->quality < 7 ? 14 : 15;
142     hparams->num_last_distances_to_check =
143         params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16;
144   }
145 
146   if (params->lgwin > 24) {
147     /* Different hashers for large window brotli: not for qualities <= 2,
148        these are too fast for large window. Not for qualities >= 10: their
149        hasher already works well with large window. So the changes are:
150        H3 --> H35: for quality 3.
151        H54 --> H55: for quality 4 with size hint > 1MB
152        H6 --> H65: for qualities 5, 6, 7, 8, 9. */
153     if (hparams->type == 3) {
154       hparams->type = 35;
155     }
156     if (hparams->type == 54) {
157       hparams->type = 55;
158     }
159     if (hparams->type == 6) {
160       hparams->type = 65;
161     }
162   }
163 }
164 
165 #endif  /* BROTLI_ENC_QUALITY_H_ */
166