298dc153970e0120b38f63c87a2c6e8d5a78a9e7
[libav.git] / libavcodec / huffman.c
1 /**
2 * @file huffman.c
3 * huffman tree builder and VLC generator
4 * Copyright (c) 2006 Konstantin Shishkov
5 *
6 * This file is part of FFmpeg.
7 *
8 * FFmpeg is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * FFmpeg is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with FFmpeg; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
23 #include "avcodec.h"
24 #include "bitstream.h"
25 #include "huffman.h"
26
27 /* symbol for Huffman tree node */
28 #define HNODE -1
29
30
31 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat, Node *nodes, int node, uint32_t pfx, int pl, int *pos)
32 {
33 int s;
34
35 s = nodes[node].sym;
36 if(s != HNODE || !nodes[node].count){
37 bits[*pos] = pfx;
38 lens[*pos] = pl;
39 xlat[*pos] = s;
40 (*pos)++;
41 }else{
42 pfx <<= 1;
43 pl++;
44 get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl, pos);
45 pfx |= 1;
46 get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0+1, pfx, pl, pos);
47 }
48 }
49
50 static int build_huff_tree(VLC *vlc, Node *nodes, int head)
51 {
52 uint32_t bits[256];
53 int16_t lens[256];
54 uint8_t xlat[256];
55 int pos = 0;
56
57 get_tree_codes(bits, lens, xlat, nodes, head, 0, 0, &pos);
58 return init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
59 }
60
61
62 /**
63 * first nb_codes nodes.count must be set
64 */
65 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
66 Node nodes[2*nb_codes], huff_cmp_t cmp, int hnode_first)
67 {
68 int i, j;
69 int cur_node;
70 int64_t sum = 0;
71
72 for(i = 0; i < nb_codes; i++){
73 nodes[i].sym = i;
74 nodes[i].n0 = -2;
75 sum += nodes[i].count;
76 }
77
78 if(sum >> 31) {
79 av_log(avctx, AV_LOG_ERROR, "Too high symbol frequencies. Tree construction is not possible\n");
80 return -1;
81 }
82 qsort(nodes, nb_codes, sizeof(Node), cmp);
83 cur_node = nb_codes;
84 for(i = 0; i < nb_codes*2-1; i += 2){
85 nodes[cur_node].sym = HNODE;
86 nodes[cur_node].count = nodes[i].count + nodes[i+1].count;
87 nodes[cur_node].n0 = i;
88 for(j = cur_node; j > 0; j--){
89 if(nodes[j].count > nodes[j-1].count ||
90 (nodes[j].count == nodes[j-1].count &&
91 (!hnode_first || nodes[j].n0==j-1 || nodes[j].n0==j-2 ||
92 (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
93 break;
94 FFSWAP(Node, nodes[j], nodes[j-1]);
95 }
96 cur_node++;
97 }
98 if(build_huff_tree(vlc, nodes, nb_codes*2-2) < 0){
99 av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
100 return -1;
101 }
102 return 0;
103 }