forgejo-federation/vendor/github.com/andybalholm/brotli/metablock.go

575 lines
21 KiB
Go
Raw Normal View History

package brotli
import (
"sync"
)
/* Copyright 2014 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* Algorithms for distributing the literals and commands of a metablock between
block types and contexts. */
type metaBlockSplit struct {
literal_split blockSplit
command_split blockSplit
distance_split blockSplit
literal_context_map []uint32
literal_context_map_size uint
distance_context_map []uint32
distance_context_map_size uint
literal_histograms []histogramLiteral
literal_histograms_size uint
command_histograms []histogramCommand
command_histograms_size uint
distance_histograms []histogramDistance
distance_histograms_size uint
}
var metaBlockPool sync.Pool
func getMetaBlockSplit() *metaBlockSplit {
mb, _ := metaBlockPool.Get().(*metaBlockSplit)
if mb == nil {
mb = &metaBlockSplit{}
} else {
initBlockSplit(&mb.literal_split)
initBlockSplit(&mb.command_split)
initBlockSplit(&mb.distance_split)
mb.literal_context_map = mb.literal_context_map[:0]
mb.literal_context_map_size = 0
mb.distance_context_map = mb.distance_context_map[:0]
mb.distance_context_map_size = 0
mb.literal_histograms = mb.literal_histograms[:0]
mb.command_histograms = mb.command_histograms[:0]
mb.distance_histograms = mb.distance_histograms[:0]
}
return mb
}
func freeMetaBlockSplit(mb *metaBlockSplit) {
metaBlockPool.Put(mb)
}
func initDistanceParams(params *encoderParams, npostfix uint32, ndirect uint32) {
var dist_params *distanceParams = &params.dist
var alphabet_size uint32
var max_distance uint32
dist_params.distance_postfix_bits = npostfix
dist_params.num_direct_distance_codes = ndirect
alphabet_size = uint32(distanceAlphabetSize(uint(npostfix), uint(ndirect), maxDistanceBits))
max_distance = ndirect + (1 << (maxDistanceBits + npostfix + 2)) - (1 << (npostfix + 2))
if params.large_window {
var bound = [maxNpostfix + 1]uint32{0, 4, 12, 28}
var postfix uint32 = 1 << npostfix
alphabet_size = uint32(distanceAlphabetSize(uint(npostfix), uint(ndirect), largeMaxDistanceBits))
/* The maximum distance is set so that no distance symbol used can encode
a distance larger than BROTLI_MAX_ALLOWED_DISTANCE with all
its extra bits set. */
if ndirect < bound[npostfix] {
max_distance = maxAllowedDistance - (bound[npostfix] - ndirect)
} else if ndirect >= bound[npostfix]+postfix {
max_distance = (3 << 29) - 4 + (ndirect - bound[npostfix])
} else {
max_distance = maxAllowedDistance
}
}
dist_params.alphabet_size = alphabet_size
dist_params.max_distance = uint(max_distance)
}
func recomputeDistancePrefixes(cmds []command, orig_params *distanceParams, new_params *distanceParams) {
if orig_params.distance_postfix_bits == new_params.distance_postfix_bits && orig_params.num_direct_distance_codes == new_params.num_direct_distance_codes {
return
}
for i := range cmds {
var cmd *command = &cmds[i]
if commandCopyLen(cmd) != 0 && cmd.cmd_prefix_ >= 128 {
prefixEncodeCopyDistance(uint(commandRestoreDistanceCode(cmd, orig_params)), uint(new_params.num_direct_distance_codes), uint(new_params.distance_postfix_bits), &cmd.dist_prefix_, &cmd.dist_extra_)
}
}
}
func computeDistanceCost(cmds []command, orig_params *distanceParams, new_params *distanceParams, cost *float64) bool {
var equal_params bool = false
var dist_prefix uint16
var dist_extra uint32
var extra_bits float64 = 0.0
var histo histogramDistance
histogramClearDistance(&histo)
if orig_params.distance_postfix_bits == new_params.distance_postfix_bits && orig_params.num_direct_distance_codes == new_params.num_direct_distance_codes {
equal_params = true
}
for i := range cmds {
cmd := &cmds[i]
if commandCopyLen(cmd) != 0 && cmd.cmd_prefix_ >= 128 {
if equal_params {
dist_prefix = cmd.dist_prefix_
} else {
var distance uint32 = commandRestoreDistanceCode(cmd, orig_params)
if distance > uint32(new_params.max_distance) {
return false
}
prefixEncodeCopyDistance(uint(distance), uint(new_params.num_direct_distance_codes), uint(new_params.distance_postfix_bits), &dist_prefix, &dist_extra)
}
histogramAddDistance(&histo, uint(dist_prefix)&0x3FF)
extra_bits += float64(dist_prefix >> 10)
}
}
*cost = populationCostDistance(&histo) + extra_bits
return true
}
var buildMetaBlock_kMaxNumberOfHistograms uint = 256
func buildMetaBlock(ringbuffer []byte, pos uint, mask uint, params *encoderParams, prev_byte byte, prev_byte2 byte, cmds []command, literal_context_mode int, mb *metaBlockSplit) {
var distance_histograms []histogramDistance
var literal_histograms []histogramLiteral
var literal_context_modes []int = nil
var literal_histograms_size uint
var distance_histograms_size uint
var i uint
var literal_context_multiplier uint = 1
var npostfix uint32
var ndirect_msb uint32 = 0
var check_orig bool = true
var best_dist_cost float64 = 1e99
var orig_params encoderParams = *params
/* Histogram ids need to fit in one byte. */
var new_params encoderParams = *params
for npostfix = 0; npostfix <= maxNpostfix; npostfix++ {
for ; ndirect_msb < 16; ndirect_msb++ {
var ndirect uint32 = ndirect_msb << npostfix
var skip bool
var dist_cost float64
initDistanceParams(&new_params, npostfix, ndirect)
if npostfix == orig_params.dist.distance_postfix_bits && ndirect == orig_params.dist.num_direct_distance_codes {
check_orig = false
}
skip = !computeDistanceCost(cmds, &orig_params.dist, &new_params.dist, &dist_cost)
if skip || (dist_cost > best_dist_cost) {
break
}
best_dist_cost = dist_cost
params.dist = new_params.dist
}
if ndirect_msb > 0 {
ndirect_msb--
}
ndirect_msb /= 2
}
if check_orig {
var dist_cost float64
computeDistanceCost(cmds, &orig_params.dist, &orig_params.dist, &dist_cost)
if dist_cost < best_dist_cost {
/* NB: currently unused; uncomment when more param tuning is added. */
/* best_dist_cost = dist_cost; */
params.dist = orig_params.dist
}
}
recomputeDistancePrefixes(cmds, &orig_params.dist, &params.dist)
splitBlock(cmds, ringbuffer, pos, mask, params, &mb.literal_split, &mb.command_split, &mb.distance_split)
if !params.disable_literal_context_modeling {
literal_context_multiplier = 1 << literalContextBits
literal_context_modes = make([]int, (mb.literal_split.num_types))
for i = 0; i < mb.literal_split.num_types; i++ {
literal_context_modes[i] = literal_context_mode
}
}
literal_histograms_size = mb.literal_split.num_types * literal_context_multiplier
literal_histograms = make([]histogramLiteral, literal_histograms_size)
clearHistogramsLiteral(literal_histograms, literal_histograms_size)
distance_histograms_size = mb.distance_split.num_types << distanceContextBits
distance_histograms = make([]histogramDistance, distance_histograms_size)
clearHistogramsDistance(distance_histograms, distance_histograms_size)
mb.command_histograms_size = mb.command_split.num_types
if cap(mb.command_histograms) < int(mb.command_histograms_size) {
mb.command_histograms = make([]histogramCommand, (mb.command_histograms_size))
} else {
mb.command_histograms = mb.command_histograms[:mb.command_histograms_size]
}
clearHistogramsCommand(mb.command_histograms, mb.command_histograms_size)
buildHistogramsWithContext(cmds, &mb.literal_split, &mb.command_split, &mb.distance_split, ringbuffer, pos, mask, prev_byte, prev_byte2, literal_context_modes, literal_histograms, mb.command_histograms, distance_histograms)
literal_context_modes = nil
mb.literal_context_map_size = mb.literal_split.num_types << literalContextBits
if cap(mb.literal_context_map) < int(mb.literal_context_map_size) {
mb.literal_context_map = make([]uint32, (mb.literal_context_map_size))
} else {
mb.literal_context_map = mb.literal_context_map[:mb.literal_context_map_size]
}
mb.literal_histograms_size = mb.literal_context_map_size
if cap(mb.literal_histograms) < int(mb.literal_histograms_size) {
mb.literal_histograms = make([]histogramLiteral, (mb.literal_histograms_size))
} else {
mb.literal_histograms = mb.literal_histograms[:mb.literal_histograms_size]
}
clusterHistogramsLiteral(literal_histograms, literal_histograms_size, buildMetaBlock_kMaxNumberOfHistograms, mb.literal_histograms, &mb.literal_histograms_size, mb.literal_context_map)
literal_histograms = nil
if params.disable_literal_context_modeling {
/* Distribute assignment to all contexts. */
for i = mb.literal_split.num_types; i != 0; {
var j uint = 0
i--
for ; j < 1<<literalContextBits; j++ {
mb.literal_context_map[(i<<literalContextBits)+j] = mb.literal_context_map[i]
}
}
}
mb.distance_context_map_size = mb.distance_split.num_types << distanceContextBits
if cap(mb.distance_context_map) < int(mb.distance_context_map_size) {
mb.distance_context_map = make([]uint32, (mb.distance_context_map_size))
} else {
mb.distance_context_map = mb.distance_context_map[:mb.distance_context_map_size]
}
mb.distance_histograms_size = mb.distance_context_map_size
if cap(mb.distance_histograms) < int(mb.distance_histograms_size) {
mb.distance_histograms = make([]histogramDistance, (mb.distance_histograms_size))
} else {
mb.distance_histograms = mb.distance_histograms[:mb.distance_histograms_size]
}
clusterHistogramsDistance(distance_histograms, mb.distance_context_map_size, buildMetaBlock_kMaxNumberOfHistograms, mb.distance_histograms, &mb.distance_histograms_size, mb.distance_context_map)
distance_histograms = nil
}
const maxStaticContexts = 13
/* Greedy block splitter for one block category (literal, command or distance).
Gathers histograms for all context buckets. */
type contextBlockSplitter struct {
alphabet_size_ uint
num_contexts_ uint
max_block_types_ uint
min_block_size_ uint
split_threshold_ float64
num_blocks_ uint
split_ *blockSplit
histograms_ []histogramLiteral
histograms_size_ *uint
target_block_size_ uint
block_size_ uint
curr_histogram_ix_ uint
last_histogram_ix_ [2]uint
last_entropy_ [2 * maxStaticContexts]float64
merge_last_count_ uint
}
func initContextBlockSplitter(self *contextBlockSplitter, alphabet_size uint, num_contexts uint, min_block_size uint, split_threshold float64, num_symbols uint, split *blockSplit, histograms *[]histogramLiteral, histograms_size *uint) {
var max_num_blocks uint = num_symbols/min_block_size + 1
var max_num_types uint
assert(num_contexts <= maxStaticContexts)
self.alphabet_size_ = alphabet_size
self.num_contexts_ = num_contexts
self.max_block_types_ = maxNumberOfBlockTypes / num_contexts
self.min_block_size_ = min_block_size
self.split_threshold_ = split_threshold
self.num_blocks_ = 0
self.split_ = split
self.histograms_size_ = histograms_size
self.target_block_size_ = min_block_size
self.block_size_ = 0
self.curr_histogram_ix_ = 0
self.merge_last_count_ = 0
/* We have to allocate one more histogram than the maximum number of block
types for the current histogram when the meta-block is too big. */
max_num_types = brotli_min_size_t(max_num_blocks, self.max_block_types_+1)
brotli_ensure_capacity_uint8_t(&split.types, &split.types_alloc_size, max_num_blocks)
brotli_ensure_capacity_uint32_t(&split.lengths, &split.lengths_alloc_size, max_num_blocks)
split.num_blocks = max_num_blocks
*histograms_size = max_num_types * num_contexts
if histograms == nil || cap(*histograms) < int(*histograms_size) {
*histograms = make([]histogramLiteral, (*histograms_size))
} else {
*histograms = (*histograms)[:*histograms_size]
}
self.histograms_ = *histograms
/* Clear only current histogram. */
clearHistogramsLiteral(self.histograms_[0:], num_contexts)
self.last_histogram_ix_[1] = 0
self.last_histogram_ix_[0] = self.last_histogram_ix_[1]
}
/* Does either of three things:
(1) emits the current block with a new block type;
(2) emits the current block with the type of the second last block;
(3) merges the current block with the last block. */
func contextBlockSplitterFinishBlock(self *contextBlockSplitter, is_final bool) {
var split *blockSplit = self.split_
var num_contexts uint = self.num_contexts_
var last_entropy []float64 = self.last_entropy_[:]
var histograms []histogramLiteral = self.histograms_
if self.block_size_ < self.min_block_size_ {
self.block_size_ = self.min_block_size_
}
if self.num_blocks_ == 0 {
var i uint
/* Create first block. */
split.lengths[0] = uint32(self.block_size_)
split.types[0] = 0
for i = 0; i < num_contexts; i++ {
last_entropy[i] = bitsEntropy(histograms[i].data_[:], self.alphabet_size_)
last_entropy[num_contexts+i] = last_entropy[i]
}
self.num_blocks_++
split.num_types++
self.curr_histogram_ix_ += num_contexts
if self.curr_histogram_ix_ < *self.histograms_size_ {
clearHistogramsLiteral(self.histograms_[self.curr_histogram_ix_:], self.num_contexts_)
}
self.block_size_ = 0
} else if self.block_size_ > 0 {
var entropy [maxStaticContexts]float64
var combined_histo []histogramLiteral = make([]histogramLiteral, (2 * num_contexts))
var combined_entropy [2 * maxStaticContexts]float64
var diff = [2]float64{0.0}
/* Try merging the set of histograms for the current block type with the
respective set of histograms for the last and second last block types.
Decide over the split based on the total reduction of entropy across
all contexts. */
var i uint
for i = 0; i < num_contexts; i++ {
var curr_histo_ix uint = self.curr_histogram_ix_ + i
var j uint
entropy[i] = bitsEntropy(histograms[curr_histo_ix].data_[:], self.alphabet_size_)
for j = 0; j < 2; j++ {
var jx uint = j*num_contexts + i
var last_histogram_ix uint = self.last_histogram_ix_[j] + i
combined_histo[jx] = histograms[curr_histo_ix]
histogramAddHistogramLiteral(&combined_histo[jx], &histograms[last_histogram_ix])
combined_entropy[jx] = bitsEntropy(combined_histo[jx].data_[0:], self.alphabet_size_)
diff[j] += combined_entropy[jx] - entropy[i] - last_entropy[jx]
}
}
if split.num_types < self.max_block_types_ && diff[0] > self.split_threshold_ && diff[1] > self.split_threshold_ {
/* Create new block. */
split.lengths[self.num_blocks_] = uint32(self.block_size_)
split.types[self.num_blocks_] = byte(split.num_types)
self.last_histogram_ix_[1] = self.last_histogram_ix_[0]
self.last_histogram_ix_[0] = split.num_types * num_contexts
for i = 0; i < num_contexts; i++ {
last_entropy[num_contexts+i] = last_entropy[i]
last_entropy[i] = entropy[i]
}
self.num_blocks_++
split.num_types++
self.curr_histogram_ix_ += num_contexts
if self.curr_histogram_ix_ < *self.histograms_size_ {
clearHistogramsLiteral(self.histograms_[self.curr_histogram_ix_:], self.num_contexts_)
}
self.block_size_ = 0
self.merge_last_count_ = 0
self.target_block_size_ = self.min_block_size_
} else if diff[1] < diff[0]-20.0 {
split.lengths[self.num_blocks_] = uint32(self.block_size_)
split.types[self.num_blocks_] = split.types[self.num_blocks_-2]
/* Combine this block with second last block. */
var tmp uint = self.last_histogram_ix_[0]
self.last_histogram_ix_[0] = self.last_histogram_ix_[1]
self.last_histogram_ix_[1] = tmp
for i = 0; i < num_contexts; i++ {
histograms[self.last_histogram_ix_[0]+i] = combined_histo[num_contexts+i]
last_entropy[num_contexts+i] = last_entropy[i]
last_entropy[i] = combined_entropy[num_contexts+i]
histogramClearLiteral(&histograms[self.curr_histogram_ix_+i])
}
self.num_blocks_++
self.block_size_ = 0
self.merge_last_count_ = 0
self.target_block_size_ = self.min_block_size_
} else {
/* Combine this block with last block. */
split.lengths[self.num_blocks_-1] += uint32(self.block_size_)
for i = 0; i < num_contexts; i++ {
histograms[self.last_histogram_ix_[0]+i] = combined_histo[i]
last_entropy[i] = combined_entropy[i]
if split.num_types == 1 {
last_entropy[num_contexts+i] = last_entropy[i]
}
histogramClearLiteral(&histograms[self.curr_histogram_ix_+i])
}
self.block_size_ = 0
self.merge_last_count_++
if self.merge_last_count_ > 1 {
self.target_block_size_ += self.min_block_size_
}
}
combined_histo = nil
}
if is_final {
*self.histograms_size_ = split.num_types * num_contexts
split.num_blocks = self.num_blocks_
}
}
/* Adds the next symbol to the current block type and context. When the
current block reaches the target size, decides on merging the block. */
func contextBlockSplitterAddSymbol(self *contextBlockSplitter, symbol uint, context uint) {
histogramAddLiteral(&self.histograms_[self.curr_histogram_ix_+context], symbol)
self.block_size_++
if self.block_size_ == self.target_block_size_ {
contextBlockSplitterFinishBlock(self, false) /* is_final = */
}
}
func mapStaticContexts(num_contexts uint, static_context_map []uint32, mb *metaBlockSplit) {
var i uint
mb.literal_context_map_size = mb.literal_split.num_types << literalContextBits
if cap(mb.literal_context_map) < int(mb.literal_context_map_size) {
mb.literal_context_map = make([]uint32, (mb.literal_context_map_size))
} else {
mb.literal_context_map = mb.literal_context_map[:mb.literal_context_map_size]
}
for i = 0; i < mb.literal_split.num_types; i++ {
var offset uint32 = uint32(i * num_contexts)
var j uint
for j = 0; j < 1<<literalContextBits; j++ {
mb.literal_context_map[(i<<literalContextBits)+j] = offset + static_context_map[j]
}
}
}
func buildMetaBlockGreedyInternal(ringbuffer []byte, pos uint, mask uint, prev_byte byte, prev_byte2 byte, literal_context_lut contextLUT, num_contexts uint, static_context_map []uint32, commands []command, mb *metaBlockSplit) {
var lit_blocks struct {
plain blockSplitterLiteral
ctx contextBlockSplitter
}
var cmd_blocks blockSplitterCommand
var dist_blocks blockSplitterDistance
var num_literals uint = 0
for i := range commands {
num_literals += uint(commands[i].insert_len_)
}
if num_contexts == 1 {
initBlockSplitterLiteral(&lit_blocks.plain, 256, 512, 400.0, num_literals, &mb.literal_split, &mb.literal_histograms, &mb.literal_histograms_size)
} else {
initContextBlockSplitter(&lit_blocks.ctx, 256, num_contexts, 512, 400.0, num_literals, &mb.literal_split, &mb.literal_histograms, &mb.literal_histograms_size)
}
initBlockSplitterCommand(&cmd_blocks, numCommandSymbols, 1024, 500.0, uint(len(commands)), &mb.command_split, &mb.command_histograms, &mb.command_histograms_size)
initBlockSplitterDistance(&dist_blocks, 64, 512, 100.0, uint(len(commands)), &mb.distance_split, &mb.distance_histograms, &mb.distance_histograms_size)
for _, cmd := range commands {
var j uint
blockSplitterAddSymbolCommand(&cmd_blocks, uint(cmd.cmd_prefix_))
for j = uint(cmd.insert_len_); j != 0; j-- {
var literal byte = ringbuffer[pos&mask]
if num_contexts == 1 {
blockSplitterAddSymbolLiteral(&lit_blocks.plain, uint(literal))
} else {
var context uint = uint(getContext(prev_byte, prev_byte2, literal_context_lut))
contextBlockSplitterAddSymbol(&lit_blocks.ctx, uint(literal), uint(static_context_map[context]))
}
prev_byte2 = prev_byte
prev_byte = literal
pos++
}
pos += uint(commandCopyLen(&cmd))
if commandCopyLen(&cmd) != 0 {
prev_byte2 = ringbuffer[(pos-2)&mask]
prev_byte = ringbuffer[(pos-1)&mask]
if cmd.cmd_prefix_ >= 128 {
blockSplitterAddSymbolDistance(&dist_blocks, uint(cmd.dist_prefix_)&0x3FF)
}
}
}
if num_contexts == 1 {
blockSplitterFinishBlockLiteral(&lit_blocks.plain, true) /* is_final = */
} else {
contextBlockSplitterFinishBlock(&lit_blocks.ctx, true) /* is_final = */
}
blockSplitterFinishBlockCommand(&cmd_blocks, true) /* is_final = */
blockSplitterFinishBlockDistance(&dist_blocks, true) /* is_final = */
if num_contexts > 1 {
mapStaticContexts(num_contexts, static_context_map, mb)
}
}
func buildMetaBlockGreedy(ringbuffer []byte, pos uint, mask uint, prev_byte byte, prev_byte2 byte, literal_context_lut contextLUT, num_contexts uint, static_context_map []uint32, commands []command, mb *metaBlockSplit) {
if num_contexts == 1 {
buildMetaBlockGreedyInternal(ringbuffer, pos, mask, prev_byte, prev_byte2, literal_context_lut, 1, nil, commands, mb)
} else {
buildMetaBlockGreedyInternal(ringbuffer, pos, mask, prev_byte, prev_byte2, literal_context_lut, num_contexts, static_context_map, commands, mb)
}
}
func optimizeHistograms(num_distance_codes uint32, mb *metaBlockSplit) {
var good_for_rle [numCommandSymbols]byte
var i uint
for i = 0; i < mb.literal_histograms_size; i++ {
optimizeHuffmanCountsForRLE(256, mb.literal_histograms[i].data_[:], good_for_rle[:])
}
for i = 0; i < mb.command_histograms_size; i++ {
optimizeHuffmanCountsForRLE(numCommandSymbols, mb.command_histograms[i].data_[:], good_for_rle[:])
}
for i = 0; i < mb.distance_histograms_size; i++ {
optimizeHuffmanCountsForRLE(uint(num_distance_codes), mb.distance_histograms[i].data_[:], good_for_rle[:])
}
}