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. */
36static 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
47static 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. */
54static BROTLI_INLINE size_t MaxZopfliCandidates(
55  const BrotliEncoderParams* params) {
56  return params->quality <= 10 ? 1 : 5;
57}
58
59static 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. */
75static 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. */
99static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
100  return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
101}
102
103static 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. */
116static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
117    const BrotliEncoderParams* params) {
118  return params->quality < 9 ? 64 : 512;
119}
120
121static 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