1// Copyright 2014 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package vp8l
6
7import (
8 "io"
9)
10
11// reverseBits reverses the bits in a byte.
12var reverseBits = [256]uint8{
13 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
14 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
15 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
16 0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
17 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
18 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
19 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
20 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
21 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
22 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
23 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
24 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
25 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
26 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
27 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
28 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
29}
30
31// hNode is a node in a Huffman tree.
32type hNode struct {
33 // symbol is the symbol held by this node.
34 symbol uint32
35 // children, if positive, is the hTree.nodes index of the first of
36 // this node's two children. Zero means an uninitialized node,
37 // and -1 means a leaf node.
38 children int32
39}
40
41const leafNode = -1
42
43// lutSize is the log-2 size of an hTree's look-up table.
44const lutSize, lutMask = 7, 1<<7 - 1
45
46// hTree is a Huffman tree.
47type hTree struct {
48 // nodes are the nodes of the Huffman tree. During construction,
49 // len(nodes) grows from 1 up to cap(nodes) by steps of two.
50 // After construction, len(nodes) == cap(nodes), and both equal
51 // 2*theNumberOfSymbols - 1.
52 nodes []hNode
53 // lut is a look-up table for walking the nodes. The x in lut[x] is
54 // the next lutSize bits in the bit-stream. The low 8 bits of lut[x]
55 // equals 1 plus the number of bits in the next code, or 0 if the
56 // next code requires more than lutSize bits. The high 24 bits are:
57 // - the symbol, if the code requires lutSize or fewer bits, or
58 // - the hTree.nodes index to start the tree traversal from, if
59 // the next code requires more than lutSize bits.
60 lut [1 << lutSize]uint32
61}
62
63// insert inserts into the hTree a symbol whose encoding is the least
64// significant codeLength bits of code.
65func (h *hTree) insert(symbol uint32, code uint32, codeLength uint32) error {
66 if symbol > 0xffff || codeLength > 0xfe {
67 return errInvalidHuffmanTree
68 }
69 baseCode := uint32(0)
70 if codeLength > lutSize {
71 baseCode = uint32(reverseBits[(code>>(codeLength-lutSize))&0xff]) >> (8 - lutSize)
72 } else {
73 baseCode = uint32(reverseBits[code&0xff]) >> (8 - codeLength)
74 for i := 0; i < 1<<(lutSize-codeLength); i++ {
75 h.lut[baseCode|uint32(i)<<codeLength] = symbol<<8 | (codeLength + 1)
76 }
77 }
78
79 n := uint32(0)
80 for jump := lutSize; codeLength > 0; {
81 codeLength--
82 if int(n) > len(h.nodes) {
83 return errInvalidHuffmanTree
84 }
85 switch h.nodes[n].children {
86 case leafNode:
87 return errInvalidHuffmanTree
88 case 0:
89 if len(h.nodes) == cap(h.nodes) {
90 return errInvalidHuffmanTree
91 }
92 // Create two empty child nodes.
93 h.nodes[n].children = int32(len(h.nodes))
94 h.nodes = h.nodes[:len(h.nodes)+2]
95 }
96 n = uint32(h.nodes[n].children) + 1&(code>>codeLength)
97 jump--
98 if jump == 0 && h.lut[baseCode] == 0 {
99 h.lut[baseCode] = n << 8
100 }
101 }
102
103 switch h.nodes[n].children {
104 case leafNode:
105 // No-op.
106 case 0:
107 // Turn the uninitialized node into a leaf.
108 h.nodes[n].children = leafNode
109 default:
110 return errInvalidHuffmanTree
111 }
112 h.nodes[n].symbol = symbol
113 return nil
114}
115
116// codeLengthsToCodes returns the canonical Huffman codes implied by the
117// sequence of code lengths.
118func codeLengthsToCodes(codeLengths []uint32) ([]uint32, error) {
119 maxCodeLength := uint32(0)
120 for _, cl := range codeLengths {
121 if maxCodeLength < cl {
122 maxCodeLength = cl
123 }
124 }
125 const maxAllowedCodeLength = 15
126 if len(codeLengths) == 0 || maxCodeLength > maxAllowedCodeLength {
127 return nil, errInvalidHuffmanTree
128 }
129 histogram := [maxAllowedCodeLength + 1]uint32{}
130 for _, cl := range codeLengths {
131 histogram[cl]++
132 }
133 currCode, nextCodes := uint32(0), [maxAllowedCodeLength + 1]uint32{}
134 for cl := 1; cl < len(nextCodes); cl++ {
135 currCode = (currCode + histogram[cl-1]) << 1
136 nextCodes[cl] = currCode
137 }
138 codes := make([]uint32, len(codeLengths))
139 for symbol, cl := range codeLengths {
140 if cl > 0 {
141 codes[symbol] = nextCodes[cl]
142 nextCodes[cl]++
143 }
144 }
145 return codes, nil
146}
147
148// build builds a canonical Huffman tree from the given code lengths.
149func (h *hTree) build(codeLengths []uint32) error {
150 // Calculate the number of symbols.
151 var nSymbols, lastSymbol uint32
152 for symbol, cl := range codeLengths {
153 if cl != 0 {
154 nSymbols++
155 lastSymbol = uint32(symbol)
156 }
157 }
158 if nSymbols == 0 {
159 return errInvalidHuffmanTree
160 }
161 h.nodes = make([]hNode, 1, 2*nSymbols-1)
162 // Handle the trivial case.
163 if nSymbols == 1 {
164 if len(codeLengths) <= int(lastSymbol) {
165 return errInvalidHuffmanTree
166 }
167 return h.insert(lastSymbol, 0, 0)
168 }
169 // Handle the non-trivial case.
170 codes, err := codeLengthsToCodes(codeLengths)
171 if err != nil {
172 return err
173 }
174 for symbol, cl := range codeLengths {
175 if cl > 0 {
176 if err := h.insert(uint32(symbol), codes[symbol], cl); err != nil {
177 return err
178 }
179 }
180 }
181 return nil
182}
183
184// buildSimple builds a Huffman tree with 1 or 2 symbols.
185func (h *hTree) buildSimple(nSymbols uint32, symbols [2]uint32, alphabetSize uint32) error {
186 h.nodes = make([]hNode, 1, 2*nSymbols-1)
187 for i := uint32(0); i < nSymbols; i++ {
188 if symbols[i] >= alphabetSize {
189 return errInvalidHuffmanTree
190 }
191 if err := h.insert(symbols[i], i, nSymbols-1); err != nil {
192 return err
193 }
194 }
195 return nil
196}
197
198// next returns the next Huffman-encoded symbol from the bit-stream d.
199func (h *hTree) next(d *decoder) (uint32, error) {
200 var n uint32
201 // Read enough bits so that we can use the look-up table.
202 if d.nBits < lutSize {
203 c, err := d.r.ReadByte()
204 if err != nil {
205 if err == io.EOF {
206 // There are no more bytes of data, but we may still be able
207 // to read the next symbol out of the previously read bits.
208 goto slowPath
209 }
210 return 0, err
211 }
212 d.bits |= uint32(c) << d.nBits
213 d.nBits += 8
214 }
215 // Use the look-up table.
216 n = h.lut[d.bits&lutMask]
217 if b := n & 0xff; b != 0 {
218 b--
219 d.bits >>= b
220 d.nBits -= b
221 return n >> 8, nil
222 }
223 n >>= 8
224 d.bits >>= lutSize
225 d.nBits -= lutSize
226
227slowPath:
228 for h.nodes[n].children != leafNode {
229 if d.nBits == 0 {
230 c, err := d.r.ReadByte()
231 if err != nil {
232 if err == io.EOF {
233 err = io.ErrUnexpectedEOF
234 }
235 return 0, err
236 }
237 d.bits = uint32(c)
238 d.nBits = 8
239 }
240 n = uint32(h.nodes[n].children) + 1&d.bits
241 d.bits >>= 1
242 d.nBits--
243 }
244 return h.nodes[n].symbol, nil
245}