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Commit ebf35167 authored by Raph Levien's avatar Raph Levien Committed by Russ Cox
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compress/flate: Performance improvement for inflate 

Decode as much as possible of a Huffman symbol in a single table
lookup (much like the zlib implementation), filling more bits
(conservatively, so we don't consume past the end of the stream)
when the code prefix indicates more bits are needed. This
results in about a 50% performance gain in speed benchmarks.
The following set is benchcmp done on a retina MacBook Pro:

benchmark                            old MB/s     new MB/s  speedup
BenchmarkDecodeDigitsSpeed1e4           28.41        42.79    1.51x
BenchmarkDecodeDigitsSpeed1e5           30.18        47.62    1.58x
BenchmarkDecodeDigitsSpeed1e6           30.81        48.14    1.56x
BenchmarkDecodeDigitsDefault1e4         30.28        44.61    1.47x
BenchmarkDecodeDigitsDefault1e5         32.18        51.94    1.61x
BenchmarkDecodeDigitsDefault1e6         35.57        53.28    1.50x
BenchmarkDecodeDigitsCompress1e4        30.39        44.83    1.48x
BenchmarkDecodeDigitsCompress1e5        33.05        51.64    1.56x
BenchmarkDecodeDigitsCompress1e6        35.69        53.04    1.49x
BenchmarkDecodeTwainSpeed1e4            25.90        43.04    1.66x
BenchmarkDecodeTwainSpeed1e5            29.97        48.19    1.61x
BenchmarkDecodeTwainSpeed1e6            31.36        49.43    1.58x
BenchmarkDecodeTwainDefault1e4          28.79        45.02    1.56x
BenchmarkDecodeTwainDefault1e5          37.12        55.65    1.50x
BenchmarkDecodeTwainDefault1e6          39.28        58.16    1.48x
BenchmarkDecodeTwainCompress1e4         28.64        44.90    1.57x
BenchmarkDecodeTwainCompress1e5         37.40        55.98    1.50x
BenchmarkDecodeTwainCompress1e6         39.35        58.06    1.48x

R=rsc, dave, minux.ma, bradfitz, nigeltao
CC=golang-dev
https://golang.org/cl/6872063
parent c64469f8
Hide whitespace changes
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Showing with 314 additions and 209 deletions
src/pkg/compress/flate/fixedhuff.go 0 → 100644
View file @ ebf35167
package flate
// autogenerated by gen.go, DO NOT EDIT
var fixedHuffmanDecoder = huffmanDecoder{
7,
[huffmanNumChunks]uint32{
0x1007, 0x0508, 0x0108, 0x1188, 0x1107, 0x0708, 0x0308, 0x0c09,
0x1087, 0x0608, 0x0208, 0x0a09, 0x0008, 0x0808, 0x0408, 0x0e09,
0x1047, 0x0588, 0x0188, 0x0909, 0x1147, 0x0788, 0x0388, 0x0d09,
0x10c7, 0x0688, 0x0288, 0x0b09, 0x0088, 0x0888, 0x0488, 0x0f09,
0x1027, 0x0548, 0x0148, 0x11c8, 0x1127, 0x0748, 0x0348, 0x0c89,
0x10a7, 0x0648, 0x0248, 0x0a89, 0x0048, 0x0848, 0x0448, 0x0e89,
0x1067, 0x05c8, 0x01c8, 0x0989, 0x1167, 0x07c8, 0x03c8, 0x0d89,
0x10e7, 0x06c8, 0x02c8, 0x0b89, 0x00c8, 0x08c8, 0x04c8, 0x0f89,
0x1017, 0x0528, 0x0128, 0x11a8, 0x1117, 0x0728, 0x0328, 0x0c49,
0x1097, 0x0628, 0x0228, 0x0a49, 0x0028, 0x0828, 0x0428, 0x0e49,
0x1057, 0x05a8, 0x01a8, 0x0949, 0x1157, 0x07a8, 0x03a8, 0x0d49,
0x10d7, 0x06a8, 0x02a8, 0x0b49, 0x00a8, 0x08a8, 0x04a8, 0x0f49,
0x1037, 0x0568, 0x0168, 0x11e8, 0x1137, 0x0768, 0x0368, 0x0cc9,
0x10b7, 0x0668, 0x0268, 0x0ac9, 0x0068, 0x0868, 0x0468, 0x0ec9,
0x1077, 0x05e8, 0x01e8, 0x09c9, 0x1177, 0x07e8, 0x03e8, 0x0dc9,
0x10f7, 0x06e8, 0x02e8, 0x0bc9, 0x00e8, 0x08e8, 0x04e8, 0x0fc9,
0x1007, 0x0518, 0x0118, 0x1198, 0x1107, 0x0718, 0x0318, 0x0c29,
0x1087, 0x0618, 0x0218, 0x0a29, 0x0018, 0x0818, 0x0418, 0x0e29,
0x1047, 0x0598, 0x0198, 0x0929, 0x1147, 0x0798, 0x0398, 0x0d29,
0x10c7, 0x0698, 0x0298, 0x0b29, 0x0098, 0x0898, 0x0498, 0x0f29,
0x1027, 0x0558, 0x0158, 0x11d8, 0x1127, 0x0758, 0x0358, 0x0ca9,
0x10a7, 0x0658, 0x0258, 0x0aa9, 0x0058, 0x0858, 0x0458, 0x0ea9,
0x1067, 0x05d8, 0x01d8, 0x09a9, 0x1167, 0x07d8, 0x03d8, 0x0da9,
0x10e7, 0x06d8, 0x02d8, 0x0ba9, 0x00d8, 0x08d8, 0x04d8, 0x0fa9,
0x1017, 0x0538, 0x0138, 0x11b8, 0x1117, 0x0738, 0x0338, 0x0c69,
0x1097, 0x0638, 0x0238, 0x0a69, 0x0038, 0x0838, 0x0438, 0x0e69,
0x1057, 0x05b8, 0x01b8, 0x0969, 0x1157, 0x07b8, 0x03b8, 0x0d69,
0x10d7, 0x06b8, 0x02b8, 0x0b69, 0x00b8, 0x08b8, 0x04b8, 0x0f69,
0x1037, 0x0578, 0x0178, 0x11f8, 0x1137, 0x0778, 0x0378, 0x0ce9,
0x10b7, 0x0678, 0x0278, 0x0ae9, 0x0078, 0x0878, 0x0478, 0x0ee9,
0x1077, 0x05f8, 0x01f8, 0x09e9, 0x1177, 0x07f8, 0x03f8, 0x0de9,
0x10f7, 0x06f8, 0x02f8, 0x0be9, 0x00f8, 0x08f8, 0x04f8, 0x0fe9,
0x1007, 0x0508, 0x0108, 0x1188, 0x1107, 0x0708, 0x0308, 0x0c19,
0x1087, 0x0608, 0x0208, 0x0a19, 0x0008, 0x0808, 0x0408, 0x0e19,
0x1047, 0x0588, 0x0188, 0x0919, 0x1147, 0x0788, 0x0388, 0x0d19,
0x10c7, 0x0688, 0x0288, 0x0b19, 0x0088, 0x0888, 0x0488, 0x0f19,
0x1027, 0x0548, 0x0148, 0x11c8, 0x1127, 0x0748, 0x0348, 0x0c99,
0x10a7, 0x0648, 0x0248, 0x0a99, 0x0048, 0x0848, 0x0448, 0x0e99,
0x1067, 0x05c8, 0x01c8, 0x0999, 0x1167, 0x07c8, 0x03c8, 0x0d99,
0x10e7, 0x06c8, 0x02c8, 0x0b99, 0x00c8, 0x08c8, 0x04c8, 0x0f99,
0x1017, 0x0528, 0x0128, 0x11a8, 0x1117, 0x0728, 0x0328, 0x0c59,
0x1097, 0x0628, 0x0228, 0x0a59, 0x0028, 0x0828, 0x0428, 0x0e59,
0x1057, 0x05a8, 0x01a8, 0x0959, 0x1157, 0x07a8, 0x03a8, 0x0d59,
0x10d7, 0x06a8, 0x02a8, 0x0b59, 0x00a8, 0x08a8, 0x04a8, 0x0f59,
0x1037, 0x0568, 0x0168, 0x11e8, 0x1137, 0x0768, 0x0368, 0x0cd9,
0x10b7, 0x0668, 0x0268, 0x0ad9, 0x0068, 0x0868, 0x0468, 0x0ed9,
0x1077, 0x05e8, 0x01e8, 0x09d9, 0x1177, 0x07e8, 0x03e8, 0x0dd9,
0x10f7, 0x06e8, 0x02e8, 0x0bd9, 0x00e8, 0x08e8, 0x04e8, 0x0fd9,
0x1007, 0x0518, 0x0118, 0x1198, 0x1107, 0x0718, 0x0318, 0x0c39,
0x1087, 0x0618, 0x0218, 0x0a39, 0x0018, 0x0818, 0x0418, 0x0e39,
0x1047, 0x0598, 0x0198, 0x0939, 0x1147, 0x0798, 0x0398, 0x0d39,
0x10c7, 0x0698, 0x0298, 0x0b39, 0x0098, 0x0898, 0x0498, 0x0f39,
0x1027, 0x0558, 0x0158, 0x11d8, 0x1127, 0x0758, 0x0358, 0x0cb9,
0x10a7, 0x0658, 0x0258, 0x0ab9, 0x0058, 0x0858, 0x0458, 0x0eb9,
0x1067, 0x05d8, 0x01d8, 0x09b9, 0x1167, 0x07d8, 0x03d8, 0x0db9,
0x10e7, 0x06d8, 0x02d8, 0x0bb9, 0x00d8, 0x08d8, 0x04d8, 0x0fb9,
0x1017, 0x0538, 0x0138, 0x11b8, 0x1117, 0x0738, 0x0338, 0x0c79,
0x1097, 0x0638, 0x0238, 0x0a79, 0x0038, 0x0838, 0x0438, 0x0e79,
0x1057, 0x05b8, 0x01b8, 0x0979, 0x1157, 0x07b8, 0x03b8, 0x0d79,
0x10d7, 0x06b8, 0x02b8, 0x0b79, 0x00b8, 0x08b8, 0x04b8, 0x0f79,
0x1037, 0x0578, 0x0178, 0x11f8, 0x1137, 0x0778, 0x0378, 0x0cf9,
0x10b7, 0x0678, 0x0278, 0x0af9, 0x0078, 0x0878, 0x0478, 0x0ef9,
0x1077, 0x05f8, 0x01f8, 0x09f9, 0x1177, 0x07f8, 0x03f8, 0x0df9,
0x10f7, 0x06f8, 0x02f8, 0x0bf9, 0x00f8, 0x08f8, 0x04f8, 0x0ff9,
},
nil, 0,
}
src/pkg/compress/flate/flate_test.go
View file @ ebf35167
......@@ -10,122 +10,9 @@ package flate
import (
"bytes"
"reflect"
"testing"
)
// The Huffman code lengths used by the fixed-format Huffman blocks.
var fixedHuffmanBits = [...]int{
// 0-143 length 8
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
// 144-255 length 9
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
// 256-279 length 7
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7,
// 280-287 length 8
8, 8, 8, 8, 8, 8, 8, 8,
}
type InitDecoderTest struct {
in []int
out huffmanDecoder
ok bool
}
var initDecoderTests = []*InitDecoderTest{
// Example from Connell 1973,
{
[]int{3, 5, 2, 4, 3, 5, 5, 4, 4, 3, 4, 5},
huffmanDecoder{
2, 5,
[maxCodeLen + 1]int{2: 0, 4, 13, 31},
[maxCodeLen + 1]int{2: 0, 1, 6, 20},
// Paper used different code assignment:
// 2, 9, 4, 0, 10, 8, 3, 7, 1, 5, 11, 6
// Reordered here so that codes of same length
// are assigned to increasing numbers.
[]int{2, 0, 4, 9, 3, 7, 8, 10, 1, 5, 6, 11},
},
true,
},
// Example from RFC 1951 section 3.2.2
{
[]int{2, 1, 3, 3},
huffmanDecoder{
1, 3,
[maxCodeLen + 1]int{1: 0, 2, 7},
[maxCodeLen + 1]int{1: 0, 1, 4},
[]int{1, 0, 2, 3},
},
true,
},
// Second example from RFC 1951 section 3.2.2
{
[]int{3, 3, 3, 3, 3, 2, 4, 4},
huffmanDecoder{
2, 4,
[maxCodeLen + 1]int{2: 0, 6, 15},
[maxCodeLen + 1]int{2: 0, 1, 8},
[]int{5, 0, 1, 2, 3, 4, 6, 7},
},
true,
},
// Static Huffman codes (RFC 1951 section 3.2.6)
{
fixedHuffmanBits[0:],
fixedHuffmanDecoder,
true,
},
// Illegal input.
{
[]int{},
huffmanDecoder{},
false,
},
// Illegal input.
{
[]int{0, 0, 0, 0, 0, 0, 0},
huffmanDecoder{},
false,
},
}
func TestInitDecoder(t *testing.T) {
for i, tt := range initDecoderTests {
var h huffmanDecoder
if h.init(tt.in) != tt.ok {
t.Errorf("test %d: init = %v", i, !tt.ok)
continue
}
if !reflect.DeepEqual(&h, &tt.out) {
t.Errorf("test %d:\nhave %v\nwant %v", i, h, tt.out)
}
}
}
func TestUncompressedSource(t *testing.T) {
decoder := NewReader(bytes.NewBuffer([]byte{0x01, 0x01, 0x00, 0xfe, 0xff, 0x11}))
output := make([]byte, 1)
......
src/pkg/compress/flate/gen.go 0 → 100644
View file @ ebf35167
// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build ignore
// This program generates fixedhuff.go
// Invoke as
//
// go run gen.go |gofmt >fixedhuff.go
package main
import (
"fmt"
)
const maxCodeLen = 16
// Note: the definition of the huffmanDecoder struct is copied from
// inflate.go, as it is private to the implementation.
// chunk & 15 is number of bits
// chunk >> 4 is value, including table link
const (
huffmanChunkBits = 9
huffmanNumChunks = 1 << huffmanChunkBits
huffmanCountMask = 15
huffmanValueShift = 4
)
type huffmanDecoder struct {
min int // the minimum code length
chunks [huffmanNumChunks]uint32 // chunks as described above
links [][]uint32 // overflow links
linkMask uint32 // mask the width of the link table
}
// Initialize Huffman decoding tables from array of code lengths.
func (h *huffmanDecoder) init(bits []int) bool {
// Count number of codes of each length,
// compute min and max length.
var count [maxCodeLen]int
var min, max int
for _, n := range bits {
if n == 0 {
continue
}
if min == 0 || n < min {
min = n
}
if n > max {
max = n
}
count[n]++
}
if max == 0 {
return false
}
h.min = min
var linkBits uint
var numLinks int
if max > huffmanChunkBits {
linkBits = uint(max) - huffmanChunkBits
numLinks = 1 << linkBits
h.linkMask = uint32(numLinks - 1)
}
code := 0
var nextcode [maxCodeLen]int
for i := min; i <= max; i++ {
if i == huffmanChunkBits+1 {
// create link tables
link := code >> 1
h.links = make([][]uint32, huffmanNumChunks-link)
for j := uint(link); j < huffmanNumChunks; j++ {
reverse := int(reverseByte[j>>8]) | int(reverseByte[j&0xff])<<8
reverse >>= uint(16 - huffmanChunkBits)
off := j - uint(link)
h.chunks[reverse] = uint32(off<<huffmanValueShift + uint(i))
h.links[off] = make([]uint32, 1<<linkBits)
}
}
n := count[i]
nextcode[i] = code
code += n
code <<= 1
}
for i, n := range bits {
if n == 0 {
continue
}
code := nextcode[n]
nextcode[n]++
chunk := uint32(i<<huffmanValueShift | n)
reverse := int(reverseByte[code>>8]) | int(reverseByte[code&0xff])<<8
reverse >>= uint(16 - n)
if n <= huffmanChunkBits {
for off := reverse; off < huffmanNumChunks; off += 1 << uint(n) {
h.chunks[off] = chunk
}
} else {
linktab := h.links[h.chunks[reverse&(huffmanNumChunks-1)]>>huffmanValueShift]
reverse >>= huffmanChunkBits
for off := reverse; off < numLinks; off += 1 << uint(n-huffmanChunkBits) {
linktab[off] = chunk
}
}
}
return true
}
func main() {
var h huffmanDecoder
var bits [288]int
initReverseByte()
for i := 0; i < 144; i++ {
bits[i] = 8
}
for i := 144; i < 256; i++ {
bits[i] = 9
}
for i := 256; i < 280; i++ {
bits[i] = 7
}
for i := 280; i < 288; i++ {
bits[i] = 8
}
h.init(bits[:])
fmt.Println("package flate")
fmt.Println()
fmt.Println("// autogenerated by gen.go, DO NOT EDIT")
fmt.Println()
fmt.Println("var fixedHuffmanDecoder = huffmanDecoder{")
fmt.Printf("\t%d,\n", h.min)
fmt.Println("\t[huffmanNumChunks]uint32{")
for i := 0; i < huffmanNumChunks; i++ {
if i&7 == 0 {
fmt.Printf("\t\t")
} else {
fmt.Printf(" ")
}
fmt.Printf("0x%04x,", h.chunks[i])
if i&7 == 7 {
fmt.Println()
}
}
fmt.Println("\t},")
fmt.Println("\tnil, 0,")
fmt.Println("}")
}
var reverseByte [256]byte
func initReverseByte() {
for x := 0; x < 256; x++ {
var result byte
for i := uint(0); i < 8; i++ {
result |= byte(((x >> i) & 1) << (7 - i))
}
reverseByte[x] = result
}
}
src/pkg/compress/flate/inflate.go
View file @ ebf35167
......@@ -54,32 +54,46 @@ func (e *WriteError) Error() string {
return "flate: write error at offset " + strconv.FormatInt(e.Offset, 10) + ": " + e.Err.Error()
}
// Huffman decoder is based on
// J. Brian Connell, ``A Huffman-Shannon-Fano Code,''
// Proceedings of the IEEE, 61(7) (July 1973), pp 1046-1047.
type huffmanDecoder struct {
// min, max code length
min, max int
// limit[i] = largest code word of length i
// Given code v of length n,
// need more bits if v > limit[n].
limit [maxCodeLen + 1]int
// Note that much of the implemenation of huffmanDecoder is also copied
// into gen.go (in package main) for the purpose of precomputing the
// fixed huffman tables so they can be included statically.
// The data structure for decoding Huffman tables is based on that of
// zlib. There is a lookup table of a fixed bit width (huffmanChunkBits),
// For codes smaller than the table width, there are multiple entries
// (each combination of trailing bits has the same value). For codes
// larger than the table width, the table contains a link to an overflow
// table. The width of each entry in the link table is the maximum code
// size minus the chunk width.
// Note that you can do a lookup in the table even without all bits
// filled. Since the extra bits are zero, and the DEFLATE Huffman codes
// have the property that shorter codes come before longer ones, the
// bit length estimate in the result is a lower bound on the actual
// number of bits.
// chunk & 15 is number of bits
// chunk >> 4 is value, including table link
// base[i] = smallest code word of length i - seq number
base [maxCodeLen + 1]int
const (
huffmanChunkBits = 9
huffmanNumChunks = 1 << huffmanChunkBits
huffmanCountMask = 15
huffmanValueShift = 4
)
// codes[seq number] = output code.
// Given code v of length n, value is
// codes[v - base[n]].
codes []int
type huffmanDecoder struct {
min int // the minimum code length
chunks [huffmanNumChunks]uint32 // chunks as described above
links [][]uint32 // overflow links
linkMask uint32 // mask the width of the link table
}
// Initialize Huffman decoding tables from array of code lengths.
func (h *huffmanDecoder) init(bits []int) bool {
// Count number of codes of each length,
// compute min and max length.
var count [maxCodeLen + 1]int
var count [maxCodeLen]int
var min, max int
for _, n := range bits {
if n == 0 {
......@@ -98,93 +112,58 @@ func (h *huffmanDecoder) init(bits []int) bool {
}
h.min = min
h.max = max
// For each code range, compute
// nextcode (first code of that length),
// limit (last code of that length), and
// base (offset from first code to sequence number).
var linkBits uint
var numLinks int
if max > huffmanChunkBits {
linkBits = uint(max) - huffmanChunkBits
numLinks = 1 << linkBits
h.linkMask = uint32(numLinks - 1)
}
code := 0
seq := 0
var nextcode [maxCodeLen]int
for i := min; i <= max; i++ {
if i == huffmanChunkBits+1 {
// create link tables
link := code >> 1
h.links = make([][]uint32, huffmanNumChunks-link)
for j := uint(link); j < huffmanNumChunks; j++ {
reverse := int(reverseByte[j>>8]) | int(reverseByte[j&0xff])<<8
reverse >>= uint(16 - huffmanChunkBits)
off := j - uint(link)
h.chunks[reverse] = uint32(off<<huffmanValueShift + uint(i))
h.links[off] = make([]uint32, 1<<linkBits)
}
}
n := count[i]
nextcode[i] = code
h.base[i] = code - seq
code += n
seq += n
h.limit[i] = code - 1
code <<= 1
}
// Make array mapping sequence numbers to codes.
if len(h.codes) < len(bits) {
h.codes = make([]int, len(bits))
}
for i, n := range bits {
if n == 0 {
continue
}
code := nextcode[n]
nextcode[n]++
seq := code - h.base[n]
h.codes[seq] = i
chunk := uint32(i<<huffmanValueShift | n)
reverse := int(reverseByte[code>>8]) | int(reverseByte[code&0xff])<<8
reverse >>= uint(16 - n)
if n <= huffmanChunkBits {
for off := reverse; off < huffmanNumChunks; off += 1 << uint(n) {
h.chunks[off] = chunk
}
} else {
linktab := h.links[h.chunks[reverse&(huffmanNumChunks-1)]>>huffmanValueShift]
reverse >>= huffmanChunkBits
for off := reverse; off < numLinks; off += 1 << uint(n-huffmanChunkBits) {
linktab[off] = chunk
}
}
}
return true
}
// Hard-coded Huffman tables for DEFLATE algorithm.
// See RFC 1951, section 3.2.6.
var fixedHuffmanDecoder = huffmanDecoder{
7, 9,
[maxCodeLen + 1]int{7: 23, 199, 511},
[maxCodeLen + 1]int{7: 0, 24, 224},
[]int{
// length 7: 256-279
256, 257, 258, 259, 260, 261, 262,
263, 264, 265, 266, 267, 268, 269,
270, 271, 272, 273, 274, 275, 276,
277, 278, 279,
// length 8: 0-143
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
62, 63, 64, 65, 66, 67, 68, 69, 70, 71,
72, 73, 74, 75, 76, 77, 78, 79, 80, 81,
82, 83, 84, 85, 86, 87, 88, 89, 90, 91,
92, 93, 94, 95, 96, 97, 98, 99, 100,
101, 102, 103, 104, 105, 106, 107, 108,
109, 110, 111, 112, 113, 114, 115, 116,
117, 118, 119, 120, 121, 122, 123, 124,
125, 126, 127, 128, 129, 130, 131, 132,
133, 134, 135, 136, 137, 138, 139, 140,
141, 142, 143,
// length 8: 280-287
280, 281, 282, 283, 284, 285, 286, 287,
// length 9: 144-255
144, 145, 146, 147, 148, 149, 150, 151,
152, 153, 154, 155, 156, 157, 158, 159,
160, 161, 162, 163, 164, 165, 166, 167,
168, 169, 170, 171, 172, 173, 174, 175,
176, 177, 178, 179, 180, 181, 182, 183,
184, 185, 186, 187, 188, 189, 190, 191,
192, 193, 194, 195, 196, 197, 198, 199,
200, 201, 202, 203, 204, 205, 206, 207,
208, 209, 210, 211, 212, 213, 214, 215,
216, 217, 218, 219, 220, 221, 222, 223,
224, 225, 226, 227, 228, 229, 230, 231,
232, 233, 234, 235, 236, 237, 238, 239,
240, 241, 242, 243, 244, 245, 246, 247,
248, 249, 250, 251, 252, 253, 254, 255,
},
}
// The actual read interface needed by NewReader.
// If the passed in io.Reader does not also have ReadByte,
// the NewReader will introduce its own buffering.
......@@ -644,23 +623,23 @@ func (f *decompressor) moreBits() error {
// Read the next Huffman-encoded symbol from f according to h.
func (f *decompressor) huffSym(h *huffmanDecoder) (int, error) {
for n := uint(h.min); n <= uint(h.max); n++ {
lim := h.limit[n]
if lim == -1 {
continue
}
n := uint(h.min)
for {
for f.nb < n {
if err := f.moreBits(); err != nil {
return 0, err
}
}
v := int(f.b & uint32(1<<n-1))
v <<= 16 - n
v = int(reverseByte[v>>8]) | int(reverseByte[v&0xFF])<<8 // reverse bits
if v <= lim {
chunk := h.chunks[f.b&(huffmanNumChunks-1)]
n = uint(chunk & huffmanCountMask)
if n > huffmanChunkBits {
chunk = h.links[chunk>>huffmanValueShift][(f.b>>huffmanChunkBits)&h.linkMask]
n = uint(chunk & huffmanCountMask)
}
if n <= f.nb {
f.b >>= n
f.nb -= n
return h.codes[v-h.base[n]], nil
return int(chunk >> huffmanValueShift), nil
}
}
return 0, CorruptInputError(f.roffset)
......
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