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/* 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_ */
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