/usr/share/gocode/src/github.com/bradfitz/http2/hpack/huffman.go is in golang-github-bradfitz-http2-dev 0.0~git20150509-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 | // Copyright 2014 The Go Authors.
// See https://code.google.com/p/go/source/browse/CONTRIBUTORS
// Licensed under the same terms as Go itself:
// https://code.google.com/p/go/source/browse/LICENSE
package hpack
import (
"bytes"
"io"
"sync"
)
var bufPool = sync.Pool{
New: func() interface{} { return new(bytes.Buffer) },
}
// HuffmanDecode decodes the string in v and writes the expanded
// result to w, returning the number of bytes written to w and the
// Write call's return value. At most one Write call is made.
func HuffmanDecode(w io.Writer, v []byte) (int, error) {
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
defer bufPool.Put(buf)
n := rootHuffmanNode
cur, nbits := uint(0), uint8(0)
for _, b := range v {
cur = cur<<8 | uint(b)
nbits += 8
for nbits >= 8 {
n = n.children[byte(cur>>(nbits-8))]
if n.children == nil {
buf.WriteByte(n.sym)
nbits -= n.codeLen
n = rootHuffmanNode
} else {
nbits -= 8
}
}
}
for nbits > 0 {
n = n.children[byte(cur<<(8-nbits))]
if n.children != nil || n.codeLen > nbits {
break
}
buf.WriteByte(n.sym)
nbits -= n.codeLen
n = rootHuffmanNode
}
return w.Write(buf.Bytes())
}
type node struct {
// children is non-nil for internal nodes
children []*node
// The following are only valid if children is nil:
codeLen uint8 // number of bits that led to the output of sym
sym byte // output symbol
}
func newInternalNode() *node {
return &node{children: make([]*node, 256)}
}
var rootHuffmanNode = newInternalNode()
func init() {
for i, code := range huffmanCodes {
if i > 255 {
panic("too many huffman codes")
}
addDecoderNode(byte(i), code, huffmanCodeLen[i])
}
}
func addDecoderNode(sym byte, code uint32, codeLen uint8) {
cur := rootHuffmanNode
for codeLen > 8 {
codeLen -= 8
i := uint8(code >> codeLen)
if cur.children[i] == nil {
cur.children[i] = newInternalNode()
}
cur = cur.children[i]
}
shift := 8 - codeLen
start, end := int(uint8(code<<shift)), int(1<<shift)
for i := start; i < start+end; i++ {
cur.children[i] = &node{sym: sym, codeLen: codeLen}
}
}
// AppendHuffmanString appends s, as encoded in Huffman codes, to dst
// and returns the extended buffer.
func AppendHuffmanString(dst []byte, s string) []byte {
rembits := uint8(8)
for i := 0; i < len(s); i++ {
if rembits == 8 {
dst = append(dst, 0)
}
dst, rembits = appendByteToHuffmanCode(dst, rembits, s[i])
}
if rembits < 8 {
// special EOS symbol
code := uint32(0x3fffffff)
nbits := uint8(30)
t := uint8(code >> (nbits - rembits))
dst[len(dst)-1] |= t
}
return dst
}
// HuffmanEncodeLength returns the number of bytes required to encode
// s in Huffman codes. The result is round up to byte boundary.
func HuffmanEncodeLength(s string) uint64 {
n := uint64(0)
for i := 0; i < len(s); i++ {
n += uint64(huffmanCodeLen[s[i]])
}
return (n + 7) / 8
}
// appendByteToHuffmanCode appends Huffman code for c to dst and
// returns the extended buffer and the remaining bits in the last
// element. The appending is not byte aligned and the remaining bits
// in the last element of dst is given in rembits.
func appendByteToHuffmanCode(dst []byte, rembits uint8, c byte) ([]byte, uint8) {
code := huffmanCodes[c]
nbits := huffmanCodeLen[c]
for {
if rembits > nbits {
t := uint8(code << (rembits - nbits))
dst[len(dst)-1] |= t
rembits -= nbits
break
}
t := uint8(code >> (nbits - rembits))
dst[len(dst)-1] |= t
nbits -= rembits
rembits = 8
if nbits == 0 {
break
}
dst = append(dst, 0)
}
return dst, rembits
}
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