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