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
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
|
// 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 -output fixedhuff.go
package main
import (
"bytes"
"flag"
"fmt"
"go/format"
"io/ioutil"
"log"
)
var filename = flag.String("output", "fixedhuff.go", "output file name")
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() {
flag.Parse()
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[:])
var buf bytes.Buffer
fmt.Fprintf(&buf, `// Copyright 2013 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.`+"\n\n")
fmt.Fprintln(&buf, "package flate")
fmt.Fprintln(&buf)
fmt.Fprintln(&buf, "// autogenerated by go run gen.go -output fixedhuff.go, DO NOT EDIT")
fmt.Fprintln(&buf)
fmt.Fprintln(&buf, "var fixedHuffmanDecoder = huffmanDecoder{")
fmt.Fprintf(&buf, "\t%d,\n", h.min)
fmt.Fprintln(&buf, "\t[huffmanNumChunks]uint32{")
for i := 0; i < huffmanNumChunks; i++ {
if i&7 == 0 {
fmt.Fprintf(&buf, "\t\t")
} else {
fmt.Fprintf(&buf, " ")
}
fmt.Fprintf(&buf, "0x%04x,", h.chunks[i])
if i&7 == 7 {
fmt.Fprintln(&buf)
}
}
fmt.Fprintln(&buf, "\t},")
fmt.Fprintln(&buf, "\tnil, 0,")
fmt.Fprintln(&buf, "}")
data, err := format.Source(buf.Bytes())
if err != nil {
log.Fatal(err)
}
err = ioutil.WriteFile(*filename, data, 0644)
if err != nil {
log.Fatal(err)
}
}
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
}
}
|
