154 lines
4.3 KiB
Go
154 lines
4.3 KiB
Go
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
|
|
}
|
|
}
|