huffman: add a zero_count flag and use it in fraps
[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, int no_zero_count)
32 {
33 int s;
34
35 s = nodes[node].sym;
36 if(s != HNODE || (no_zero_count && !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 no_zero_count);
46 pfx |= 1;
47 get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0+1, pfx, pl, pos,
48 no_zero_count);
49 }
50 }
51
52 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags)
53 {
54 int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
55 uint32_t bits[256];
56 int16_t lens[256];
57 uint8_t xlat[256];
58 int pos = 0;
59
60 get_tree_codes(bits, lens, xlat, nodes, head, 0, 0, &pos, no_zero_count);
61 return init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
62 }
63
64
65 /**
66 * nodes size must be 2*nb_codes
67 * first nb_codes nodes.count must be set
68 */
69 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
70 Node *nodes, huff_cmp_t cmp, int flags)
71 {
72 int i, j;
73 int cur_node;
74 int64_t sum = 0;
75
76 for(i = 0; i < nb_codes; i++){
77 nodes[i].sym = i;
78 nodes[i].n0 = -2;
79 sum += nodes[i].count;
80 }
81
82 if(sum >> 31) {
83 av_log(avctx, AV_LOG_ERROR, "Too high symbol frequencies. Tree construction is not possible\n");
84 return -1;
85 }
86 qsort(nodes, nb_codes, sizeof(Node), cmp);
87 cur_node = nb_codes;
88 nodes[nb_codes*2-1].count = 0;
89 for(i = 0; i < nb_codes*2-1; i += 2){
90 nodes[cur_node].sym = HNODE;
91 nodes[cur_node].count = nodes[i].count + nodes[i+1].count;
92 nodes[cur_node].n0 = i;
93 for(j = cur_node; j > 0; j--){
94 if(nodes[j].count > nodes[j-1].count ||
95 (nodes[j].count == nodes[j-1].count &&
96 (!(flags & FF_HUFFMAN_FLAG_HNODE_FIRST) ||
97 nodes[j].n0==j-1 || nodes[j].n0==j-2 ||
98 (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
99 break;
100 FFSWAP(Node, nodes[j], nodes[j-1]);
101 }
102 cur_node++;
103 }
104 if(build_huff_tree(vlc, nodes, nb_codes*2-2, flags) < 0){
105 av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
106 return -1;
107 }
108 return 0;
109 }