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Diffstat (limited to 'modules/brotli/enc/quality.h')
| -rw-r--r-- | modules/brotli/enc/quality.h | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/modules/brotli/enc/quality.h b/modules/brotli/enc/quality.h new file mode 100644 index 000000000..5f4d03450 --- /dev/null +++ b/modules/brotli/enc/quality.h @@ -0,0 +1,165 @@ +/* Copyright 2016 Google Inc. All Rights Reserved. + + Distributed under MIT license. + See file LICENSE for detail or copy at https://opensource.org/licenses/MIT +*/ + +/* Constants and formulas that affect speed-ratio trade-offs and thus define + quality levels. */ + +#ifndef BROTLI_ENC_QUALITY_H_ +#define BROTLI_ENC_QUALITY_H_ + +#include "../common/platform.h" +#include <brotli/encode.h> +#include "./params.h" + +#define FAST_ONE_PASS_COMPRESSION_QUALITY 0 +#define FAST_TWO_PASS_COMPRESSION_QUALITY 1 +#define ZOPFLIFICATION_QUALITY 10 +#define HQ_ZOPFLIFICATION_QUALITY 11 + +#define MAX_QUALITY_FOR_STATIC_ENTROPY_CODES 2 +#define MIN_QUALITY_FOR_BLOCK_SPLIT 4 +#define MIN_QUALITY_FOR_NONZERO_DISTANCE_PARAMS 4 +#define MIN_QUALITY_FOR_OPTIMIZE_HISTOGRAMS 4 +#define MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH 5 +#define MIN_QUALITY_FOR_CONTEXT_MODELING 5 +#define MIN_QUALITY_FOR_HQ_CONTEXT_MODELING 7 +#define MIN_QUALITY_FOR_HQ_BLOCK_SPLITTING 10 + +/* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting, + so we buffer at most this much literals and commands. */ +#define MAX_NUM_DELAYED_SYMBOLS 0x2FFF + +/* Returns hash-table size for quality levels 0 and 1. */ +static BROTLI_INLINE size_t MaxHashTableSize(int quality) { + return quality == FAST_ONE_PASS_COMPRESSION_QUALITY ? 1 << 15 : 1 << 17; +} + +/* The maximum length for which the zopflification uses distinct distances. */ +#define MAX_ZOPFLI_LEN_QUALITY_10 150 +#define MAX_ZOPFLI_LEN_QUALITY_11 325 + +/* Do not thoroughly search when a long copy is found. */ +#define BROTLI_LONG_COPY_QUICK_STEP 16384 + +static BROTLI_INLINE size_t MaxZopfliLen(const BrotliEncoderParams* params) { + return params->quality <= 10 ? + MAX_ZOPFLI_LEN_QUALITY_10 : + MAX_ZOPFLI_LEN_QUALITY_11; +} + +/* Number of best candidates to evaluate to expand Zopfli chain. */ +static BROTLI_INLINE size_t MaxZopfliCandidates( + const BrotliEncoderParams* params) { + return params->quality <= 10 ? 1 : 5; +} + +static BROTLI_INLINE void SanitizeParams(BrotliEncoderParams* params) { + params->quality = BROTLI_MIN(int, BROTLI_MAX_QUALITY, + BROTLI_MAX(int, BROTLI_MIN_QUALITY, params->quality)); + if (params->quality <= MAX_QUALITY_FOR_STATIC_ENTROPY_CODES) { + params->large_window = BROTLI_FALSE; + } + if (params->lgwin < BROTLI_MIN_WINDOW_BITS) { + params->lgwin = BROTLI_MIN_WINDOW_BITS; + } else { + int max_lgwin = params->large_window ? BROTLI_LARGE_MAX_WINDOW_BITS : + BROTLI_MAX_WINDOW_BITS; + if (params->lgwin > max_lgwin) params->lgwin = max_lgwin; + } +} + +/* Returns optimized lg_block value. */ +static BROTLI_INLINE int ComputeLgBlock(const BrotliEncoderParams* params) { + int lgblock = params->lgblock; + if (params->quality == FAST_ONE_PASS_COMPRESSION_QUALITY || + params->quality == FAST_TWO_PASS_COMPRESSION_QUALITY) { + lgblock = params->lgwin; + } else if (params->quality < MIN_QUALITY_FOR_BLOCK_SPLIT) { + lgblock = 14; + } else if (lgblock == 0) { + lgblock = 16; + if (params->quality >= 9 && params->lgwin > lgblock) { + lgblock = BROTLI_MIN(int, 18, params->lgwin); + } + } else { + lgblock = BROTLI_MIN(int, BROTLI_MAX_INPUT_BLOCK_BITS, + BROTLI_MAX(int, BROTLI_MIN_INPUT_BLOCK_BITS, lgblock)); + } + return lgblock; +} + +/* Returns log2 of the size of main ring buffer area. + Allocate at least lgwin + 1 bits for the ring buffer so that the newly + added block fits there completely and we still get lgwin bits and at least + read_block_size_bits + 1 bits because the copy tail length needs to be + smaller than ring-buffer size. */ +static BROTLI_INLINE int ComputeRbBits(const BrotliEncoderParams* params) { + return 1 + BROTLI_MAX(int, params->lgwin, params->lgblock); +} + +static BROTLI_INLINE size_t MaxMetablockSize( + const BrotliEncoderParams* params) { + int bits = + BROTLI_MIN(int, ComputeRbBits(params), BROTLI_MAX_INPUT_BLOCK_BITS); + return (size_t)1 << bits; +} + +/* When searching for backward references and have not seen matches for a long + time, we can skip some match lookups. Unsuccessful match lookups are very + expensive and this kind of a heuristic speeds up compression quite a lot. + At first 8 byte strides are taken and every second byte is put to hasher. + After 4x more literals stride by 16 bytes, every put 4-th byte to hasher. + Applied only to qualities 2 to 9. */ +static BROTLI_INLINE size_t LiteralSpreeLengthForSparseSearch( + const BrotliEncoderParams* params) { + return params->quality < 9 ? 64 : 512; +} + +static BROTLI_INLINE void ChooseHasher(const BrotliEncoderParams* params, + BrotliHasherParams* hparams) { + if (params->quality > 9) { + hparams->type = 10; + } else if (params->quality == 4 && params->size_hint >= (1 << 20)) { + hparams->type = 54; + } else if (params->quality < 5) { + hparams->type = params->quality; + } else if (params->lgwin <= 16) { + hparams->type = params->quality < 7 ? 40 : params->quality < 9 ? 41 : 42; + } else if (params->size_hint >= (1 << 20) && params->lgwin >= 19) { + hparams->type = 6; + hparams->block_bits = params->quality - 1; + hparams->bucket_bits = 15; + hparams->hash_len = 5; + hparams->num_last_distances_to_check = + params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16; + } else { + hparams->type = 5; + hparams->block_bits = params->quality - 1; + hparams->bucket_bits = params->quality < 7 ? 14 : 15; + hparams->num_last_distances_to_check = + params->quality < 7 ? 4 : params->quality < 9 ? 10 : 16; + } + + if (params->lgwin > 24) { + /* Different hashers for large window brotli: not for qualities <= 2, + these are too fast for large window. Not for qualities >= 10: their + hasher already works well with large window. So the changes are: + H3 --> H35: for quality 3. + H54 --> H55: for quality 4 with size hint > 1MB + H6 --> H65: for qualities 5, 6, 7, 8, 9. */ + if (hparams->type == 3) { + hparams->type = 35; + } + if (hparams->type == 54) { + hparams->type = 55; + } + if (hparams->type == 6) { + hparams->type = 65; + } + } +} + +#endif /* BROTLI_ENC_QUALITY_H_ */ |