huffman: use a named identifer for the bits constant
[libav.git] / libavcodec / huffman.c
CommitLineData
6168781f 1/*
437c2079 2 * Copyright (c) 2006 Konstantin Shishkov
5a582bd3 3 * Copyright (c) 2007 Loren Merritt
437c2079 4 *
2912e87a 5 * This file is part of Libav.
437c2079 6 *
2912e87a 7 * Libav is free software; you can redistribute it and/or
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8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
2912e87a 12 * Libav is distributed in the hope that it will be useful,
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13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
2912e87a 18 * License along with Libav; if not, write to the Free Software
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19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
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22/**
23 * @file
24 * huffman tree builder and VLC generator
25 */
26
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27#include <stdint.h>
28
437c2079 29#include "avcodec.h"
9106a698 30#include "get_bits.h"
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31#include "huffman.h"
32
33/* symbol for Huffman tree node */
34#define HNODE -1
35
7f9f771e 36typedef struct HeapElem {
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37 uint64_t val;
38 int name;
39} HeapElem;
40
41static void heap_sift(HeapElem *h, int root, int size)
42{
43 while (root * 2 + 1 < size) {
44 int child = root * 2 + 1;
45 if (child < size - 1 && h[child].val > h[child+1].val)
46 child++;
47 if (h[root].val > h[child].val) {
48 FFSWAP(HeapElem, h[root], h[child]);
49 root = child;
50 } else
51 break;
52 }
53}
54
55void ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats)
56{
57 HeapElem h[256];
58 int up[2*256];
59 int len[2*256];
60 int offset, i, next;
61 int size = 256;
62
63 for (offset = 1; ; offset <<= 1) {
64 for (i=0; i < size; i++) {
65 h[i].name = i;
66 h[i].val = (stats[i] << 8) + offset;
67 }
68 for (i = size / 2 - 1; i >= 0; i--)
69 heap_sift(h, i, size);
70
71 for (next = size; next < size * 2 - 1; next++) {
72 // merge the two smallest entries, and put it back in the heap
73 uint64_t min1v = h[0].val;
74 up[h[0].name] = next;
75 h[0].val = INT64_MAX;
76 heap_sift(h, 0, size);
77 up[h[0].name] = next;
78 h[0].name = next;
79 h[0].val += min1v;
80 heap_sift(h, 0, size);
81 }
82
83 len[2 * size - 2] = 0;
84 for (i = 2 * size - 3; i >= size; i--)
85 len[i] = len[up[i]] + 1;
86 for (i = 0; i < size; i++) {
87 dst[i] = len[up[i]] + 1;
88 if (dst[i] >= 32) break;
89 }
90 if (i==size) break;
91 }
92}
437c2079 93
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94static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
95 Node *nodes, int node,
96 uint32_t pfx, int pl, int *pos, int no_zero_count)
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97{
98 int s;
99
100 s = nodes[node].sym;
f76e4787 101 if (s != HNODE || (no_zero_count && !nodes[node].count)) {
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102 bits[*pos] = pfx;
103 lens[*pos] = pl;
104 xlat[*pos] = s;
105 (*pos)++;
f76e4787 106 } else {
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107 pfx <<= 1;
108 pl++;
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109 get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
110 pos, no_zero_count);
437c2079 111 pfx |= 1;
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112 get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
113 pos, no_zero_count);
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114 }
115}
116
a73cbf97 117static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags)
437c2079 118{
a73cbf97 119 int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
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120 uint32_t bits[256];
121 int16_t lens[256];
122 uint8_t xlat[256];
123 int pos = 0;
124
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125 get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
126 &pos, no_zero_count);
5a19bce2 127 return ff_init_vlc_sparse(vlc, FF_HUFFMAN_BITS, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
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128}
129
130
131/**
f1bf85b8 132 * nodes size must be 2*nb_codes
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133 * first nb_codes nodes.count must be set
134 */
135int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
3d52bca6 136 Node *nodes, HuffCmp cmp, int flags)
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137{
138 int i, j;
139 int cur_node;
140 int64_t sum = 0;
141
f76e4787 142 for (i = 0; i < nb_codes; i++) {
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143 nodes[i].sym = i;
144 nodes[i].n0 = -2;
145 sum += nodes[i].count;
146 }
147
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148 if (sum >> 31) {
149 av_log(avctx, AV_LOG_ERROR,
150 "Too high symbol frequencies. "
151 "Tree construction is not possible\n");
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152 return -1;
153 }
154 qsort(nodes, nb_codes, sizeof(Node), cmp);
155 cur_node = nb_codes;
892a4c2d 156 nodes[nb_codes*2-1].count = 0;
f76e4787 157 for (i = 0; i < nb_codes * 2 - 1; i += 2) {
437c2079 158 nodes[cur_node].sym = HNODE;
f76e4787 159 nodes[cur_node].count = nodes[i].count + nodes[i + 1].count;
437c2079 160 nodes[cur_node].n0 = i;
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161 for (j = cur_node; j > 0; j--) {
162 if (nodes[j].count > nodes[j - 1].count ||
163 (nodes[j].count == nodes[j - 1].count &&
164 (!(flags & FF_HUFFMAN_FLAG_HNODE_FIRST) ||
165 nodes[j].n0 == j - 1 || nodes[j].n0 == j - 2 ||
166 (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
437c2079 167 break;
f76e4787 168 FFSWAP(Node, nodes[j], nodes[j - 1]);
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169 }
170 cur_node++;
171 }
f76e4787 172 if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags) < 0) {
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173 av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
174 return -1;
175 }
176 return 0;
177}