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forgejo/vendor/github.com/andybalholm/brotli/block_splitter.go

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package brotli
/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* Block split point selection utilities. */
type blockSplit struct {
num_types uint
num_blocks uint
types []byte
lengths []uint32
types_alloc_size uint
lengths_alloc_size uint
}
const (
kMaxLiteralHistograms uint = 100
kMaxCommandHistograms uint = 50
kLiteralBlockSwitchCost float64 = 28.1
kCommandBlockSwitchCost float64 = 13.5
kDistanceBlockSwitchCost float64 = 14.6
kLiteralStrideLength uint = 70
kCommandStrideLength uint = 40
kSymbolsPerLiteralHistogram uint = 544
kSymbolsPerCommandHistogram uint = 530
kSymbolsPerDistanceHistogram uint = 544
kMinLengthForBlockSplitting uint = 128
kIterMulForRefining uint = 2
kMinItersForRefining uint = 100
)
func countLiterals(cmds []command, num_commands uint) uint {
var total_length uint = 0
/* Count how many we have. */
var i uint
for i = 0; i < num_commands; i++ {
total_length += uint(cmds[i].insert_len_)
}
return total_length
}
func copyLiteralsToByteArray(cmds []command, num_commands uint, data []byte, offset uint, mask uint, literals []byte) {
var pos uint = 0
var from_pos uint = offset & mask
var i uint
for i = 0; i < num_commands; i++ {
var insert_len uint = uint(cmds[i].insert_len_)
if from_pos+insert_len > mask {
var head_size uint = mask + 1 - from_pos
copy(literals[pos:], data[from_pos:][:head_size])
from_pos = 0
pos += head_size
insert_len -= head_size
}
if insert_len > 0 {
copy(literals[pos:], data[from_pos:][:insert_len])
pos += insert_len
}
from_pos = uint((uint32(from_pos+insert_len) + commandCopyLen(&cmds[i])) & uint32(mask))
}
}
func myRand(seed *uint32) uint32 {
/* Initial seed should be 7. In this case, loop length is (1 << 29). */
*seed *= 16807
return *seed
}
func bitCost(count uint) float64 {
if count == 0 {
return -2.0
} else {
return fastLog2(count)
}
}
const histogramsPerBatch = 64
const clustersPerBatch = 16
func initBlockSplit(self *blockSplit) {
self.num_types = 0
self.num_blocks = 0
self.types = nil
self.lengths = nil
self.types_alloc_size = 0
self.lengths_alloc_size = 0
}
func destroyBlockSplit(self *blockSplit) {
self.types = nil
self.lengths = nil
}
func splitBlock(cmds []command, num_commands uint, data []byte, pos uint, mask uint, params *encoderParams, literal_split *blockSplit, insert_and_copy_split *blockSplit, dist_split *blockSplit) {
{
var literals_count uint = countLiterals(cmds, num_commands)
var literals []byte = make([]byte, literals_count)
/* Create a continuous array of literals. */
copyLiteralsToByteArray(cmds, num_commands, data, pos, mask, literals)
/* Create the block split on the array of literals.
Literal histograms have alphabet size 256. */
splitByteVectorLiteral(literals, literals_count, kSymbolsPerLiteralHistogram, kMaxLiteralHistograms, kLiteralStrideLength, kLiteralBlockSwitchCost, params, literal_split)
literals = nil
}
{
var insert_and_copy_codes []uint16 = make([]uint16, num_commands)
/* Compute prefix codes for commands. */
var i uint
for i = 0; i < num_commands; i++ {
insert_and_copy_codes[i] = cmds[i].cmd_prefix_
}
/* Create the block split on the array of command prefixes. */
splitByteVectorCommand(insert_and_copy_codes, num_commands, kSymbolsPerCommandHistogram, kMaxCommandHistograms, kCommandStrideLength, kCommandBlockSwitchCost, params, insert_and_copy_split)
/* TODO: reuse for distances? */
insert_and_copy_codes = nil
}
{
var distance_prefixes []uint16 = make([]uint16, num_commands)
var j uint = 0
/* Create a continuous array of distance prefixes. */
var i uint
for i = 0; i < num_commands; i++ {
var cmd *command = &cmds[i]
if commandCopyLen(cmd) != 0 && cmd.cmd_prefix_ >= 128 {
distance_prefixes[j] = cmd.dist_prefix_ & 0x3FF
j++
}
}
/* Create the block split on the array of distance prefixes. */
splitByteVectorDistance(distance_prefixes, j, kSymbolsPerDistanceHistogram, kMaxCommandHistograms, kCommandStrideLength, kDistanceBlockSwitchCost, params, dist_split)
distance_prefixes = nil
}
}