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
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
|
// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Utilities for building and looking up Huffman trees.
//
// Author: Urvang Joshi (urvang@google.com)
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include "src/utils/huffman_utils.h"
#include "src/utils/utils.h"
#include "src/webp/format_constants.h"
// Huffman data read via DecodeImageStream is represented in two (red and green)
// bytes.
#define MAX_HTREE_GROUPS 0x10000
HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups) {
HTreeGroup* const htree_groups =
(HTreeGroup*)WebPSafeMalloc(num_htree_groups, sizeof(*htree_groups));
if (htree_groups == NULL) {
return NULL;
}
assert(num_htree_groups <= MAX_HTREE_GROUPS);
return htree_groups;
}
void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups) {
if (htree_groups != NULL) {
WebPSafeFree(htree_groups);
}
}
// Returns reverse(reverse(key, len) + 1, len), where reverse(key, len) is the
// bit-wise reversal of the len least significant bits of key.
static WEBP_INLINE uint32_t GetNextKey(uint32_t key, int len) {
uint32_t step = 1 << (len - 1);
while (key & step) {
step >>= 1;
}
return step ? (key & (step - 1)) + step : key;
}
// Stores code in table[0], table[step], table[2*step], ..., table[end].
// Assumes that end is an integer multiple of step.
static WEBP_INLINE void ReplicateValue(HuffmanCode* table,
int step, int end,
HuffmanCode code) {
assert(end % step == 0);
do {
end -= step;
table[end] = code;
} while (end > 0);
}
// Returns the table width of the next 2nd level table. count is the histogram
// of bit lengths for the remaining symbols, len is the code length of the next
// processed symbol
static WEBP_INLINE int NextTableBitSize(const int* const count,
int len, int root_bits) {
int left = 1 << (len - root_bits);
while (len < MAX_ALLOWED_CODE_LENGTH) {
left -= count[len];
if (left <= 0) break;
++len;
left <<= 1;
}
return len - root_bits;
}
// sorted[code_lengths_size] is a pre-allocated array for sorting symbols
// by code length.
static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
const int code_lengths[], int code_lengths_size,
uint16_t sorted[]) {
HuffmanCode* table = root_table; // next available space in table
int total_size = 1 << root_bits; // total size root table + 2nd level table
int len; // current code length
int symbol; // symbol index in original or sorted table
// number of codes of each length:
int count[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };
// offsets in sorted table for each length:
int offset[MAX_ALLOWED_CODE_LENGTH + 1];
assert(code_lengths_size != 0);
assert(code_lengths != NULL);
assert(root_table != NULL);
assert(root_bits > 0);
// Build histogram of code lengths.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > MAX_ALLOWED_CODE_LENGTH) {
return 0;
}
++count[code_lengths[symbol]];
}
// Error, all code lengths are zeros.
if (count[0] == code_lengths_size) {
return 0;
}
// Generate offsets into sorted symbol table by code length.
offset[1] = 0;
for (len = 1; len < MAX_ALLOWED_CODE_LENGTH; ++len) {
if (count[len] > (1 << len)) {
return 0;
}
offset[len + 1] = offset[len] + count[len];
}
// Sort symbols by length, by symbol order within each length.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
const int symbol_code_length = code_lengths[symbol];
if (code_lengths[symbol] > 0) {
sorted[offset[symbol_code_length]++] = symbol;
}
}
// Special case code with only one value.
if (offset[MAX_ALLOWED_CODE_LENGTH] == 1) {
HuffmanCode code;
code.bits = 0;
code.value = (uint16_t)sorted[0];
ReplicateValue(table, 1, total_size, code);
return total_size;
}
{
int step; // step size to replicate values in current table
uint32_t low = -1; // low bits for current root entry
uint32_t mask = total_size - 1; // mask for low bits
uint32_t key = 0; // reversed prefix code
int num_nodes = 1; // number of Huffman tree nodes
int num_open = 1; // number of open branches in current tree level
int table_bits = root_bits; // key length of current table
int table_size = 1 << table_bits; // size of current table
symbol = 0;
// Fill in root table.
for (len = 1, step = 2; len <= root_bits; ++len, step <<= 1) {
num_open <<= 1;
num_nodes += num_open;
num_open -= count[len];
if (num_open < 0) {
return 0;
}
for (; count[len] > 0; --count[len]) {
HuffmanCode code;
code.bits = (uint8_t)len;
code.value = (uint16_t)sorted[symbol++];
ReplicateValue(&table[key], step, table_size, code);
key = GetNextKey(key, len);
}
}
// Fill in 2nd level tables and add pointers to root table.
for (len = root_bits + 1, step = 2; len <= MAX_ALLOWED_CODE_LENGTH;
++len, step <<= 1) {
num_open <<= 1;
num_nodes += num_open;
num_open -= count[len];
if (num_open < 0) {
return 0;
}
for (; count[len] > 0; --count[len]) {
HuffmanCode code;
if ((key & mask) != low) {
table += table_size;
table_bits = NextTableBitSize(count, len, root_bits);
table_size = 1 << table_bits;
total_size += table_size;
low = key & mask;
root_table[low].bits = (uint8_t)(table_bits + root_bits);
root_table[low].value = (uint16_t)((table - root_table) - low);
}
code.bits = (uint8_t)(len - root_bits);
code.value = (uint16_t)sorted[symbol++];
ReplicateValue(&table[key >> root_bits], step, table_size, code);
key = GetNextKey(key, len);
}
}
// Check if tree is full.
if (num_nodes != 2 * offset[MAX_ALLOWED_CODE_LENGTH] - 1) {
return 0;
}
}
return total_size;
}
// Maximum code_lengths_size is 2328 (reached for 11-bit color_cache_bits).
// More commonly, the value is around ~280.
#define MAX_CODE_LENGTHS_SIZE \
((1 << MAX_CACHE_BITS) + NUM_LITERAL_CODES + NUM_LENGTH_CODES)
// Cut-off value for switching between heap and stack allocation.
#define SORTED_SIZE_CUTOFF 512
int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
const int code_lengths[], int code_lengths_size) {
int total_size;
assert(code_lengths_size <= MAX_CODE_LENGTHS_SIZE);
if (code_lengths_size <= SORTED_SIZE_CUTOFF) {
// use local stack-allocated array.
uint16_t sorted[SORTED_SIZE_CUTOFF];
total_size = BuildHuffmanTable(root_table, root_bits,
code_lengths, code_lengths_size, sorted);
} else { // rare case. Use heap allocation.
uint16_t* const sorted =
(uint16_t*)WebPSafeMalloc(code_lengths_size, sizeof(*sorted));
if (sorted == NULL) return 0;
total_size = BuildHuffmanTable(root_table, root_bits,
code_lengths, code_lengths_size, sorted);
WebPSafeFree(sorted);
}
return total_size;
}
|
