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package brotli
const fastOnePassCompressionQuality = 0
const fastTwoPassCompressionQuality = 1
const zopflificationQuality = 10
const hqZopflificationQuality = 11
const maxQualityForStaticEntropyCodes = 2
const minQualityForBlockSplit = 4
const minQualityForNonzeroDistanceParams = 4
const minQualityForOptimizeHistograms = 4
const minQualityForExtensiveReferenceSearch = 5
const minQualityForContextModeling = 5
const minQualityForHqContextModeling = 7
const minQualityForHqBlockSplitting = 10
/* For quality below MIN_QUALITY_FOR_BLOCK_SPLIT there is no block splitting,
so we buffer at most this much literals and commands. */
const maxNumDelayedSymbols = 0x2FFF
/* Returns hash-table size for quality levels 0 and 1. */
func maxHashTableSize(quality int) uint {
if quality == fastOnePassCompressionQuality {
return 1 << 15
} else {
return 1 << 17
}
}
/* The maximum length for which the zopflification uses distinct distances. */
const maxZopfliLenQuality10 = 150
const maxZopfliLenQuality11 = 325
/* Do not thoroughly search when a long copy is found. */
const longCopyQuickStep = 16384
func maxZopfliLen(params *encoderParams) uint {
if params.quality <= 10 {
return maxZopfliLenQuality10
} else {
return maxZopfliLenQuality11
}
}
/* Number of best candidates to evaluate to expand Zopfli chain. */
func maxZopfliCandidates(params *encoderParams) uint {
if params.quality <= 10 {
return 1
} else {
return 5
}
}
func sanitizeParams(params *encoderParams) {
params.quality = brotli_min_int(maxQuality, brotli_max_int(minQuality, params.quality))
if params.quality <= maxQualityForStaticEntropyCodes {
params.large_window = false
}
if params.lgwin < minWindowBits {
params.lgwin = minWindowBits
} else {
var max_lgwin int
if params.large_window {
max_lgwin = largeMaxWindowBits
} else {
max_lgwin = maxWindowBits
}
if params.lgwin > uint(max_lgwin) {
params.lgwin = uint(max_lgwin)
}
}
}
/* Returns optimized lg_block value. */
func computeLgBlock(params *encoderParams) int {
var lgblock int = params.lgblock
if params.quality == fastOnePassCompressionQuality || params.quality == fastTwoPassCompressionQuality {
lgblock = int(params.lgwin)
} else if params.quality < minQualityForBlockSplit {
lgblock = 14
} else if lgblock == 0 {
lgblock = 16
if params.quality >= 9 && params.lgwin > uint(lgblock) {
lgblock = brotli_min_int(18, int(params.lgwin))
}
} else {
lgblock = brotli_min_int(maxInputBlockBits, brotli_max_int(minInputBlockBits, 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. */
func computeRbBits(params *encoderParams) int {
return 1 + brotli_max_int(int(params.lgwin), params.lgblock)
}
func maxMetablockSize(params *encoderParams) uint {
var bits int = brotli_min_int(computeRbBits(params), maxInputBlockBits)
return uint(1) << uint(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. */
func literalSpreeLengthForSparseSearch(params *encoderParams) uint {
if params.quality < 9 {
return 64
} else {
return 512
}
}
func chooseHasher(params *encoderParams, hparams *hasherParams) {
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 {
if params.quality < 7 {
hparams.type_ = 40
} else if params.quality < 9 {
hparams.type_ = 41
} else {
hparams.type_ = 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
if params.quality < 7 {
hparams.num_last_distances_to_check = 4
} else if params.quality < 9 {
hparams.num_last_distances_to_check = 10
} else {
hparams.num_last_distances_to_check = 16
}
} else {
hparams.type_ = 5
hparams.block_bits = params.quality - 1
if params.quality < 7 {
hparams.bucket_bits = 14
} else {
hparams.bucket_bits = 15
}
if params.quality < 7 {
hparams.num_last_distances_to_check = 4
} else if params.quality < 9 {
hparams.num_last_distances_to_check = 10
} else {
hparams.num_last_distances_to_check = 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
}
}
}
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