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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 <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