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
34typedef 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 */
43typedef 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. */
54static 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
65static 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. */
72static BROTLI_INLINE size_t MaxZopfliCandidates(
73  const BrotliEncoderParams* params) {
74  return params->quality <= 10 ? 1 : 5;
75}
76
77static 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. */
88static 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. */
112static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) {
113  return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock);
114}
115
116static 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. */
129static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch(
130    const BrotliEncoderParams* params) {
131  return params->quality < 9 ? 64 : 512;
132}
133
134static 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