huffman.c
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1 /*
2  * Copyright (c) 2006 Konstantin Shishkov
3  *
4  * This file is part of Libav.
5  *
6  * Libav is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * Libav is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with Libav; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
26 #include "avcodec.h"
27 #include "get_bits.h"
28 #include "huffman.h"
29 
30 /* symbol for Huffman tree node */
31 #define HNODE -1
32 
33 
34 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)
35 {
36  int s;
37 
38  s = nodes[node].sym;
39  if(s != HNODE || (no_zero_count && !nodes[node].count)){
40  bits[*pos] = pfx;
41  lens[*pos] = pl;
42  xlat[*pos] = s;
43  (*pos)++;
44  }else{
45  pfx <<= 1;
46  pl++;
47  get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl, pos,
48  no_zero_count);
49  pfx |= 1;
50  get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0+1, pfx, pl, pos,
51  no_zero_count);
52  }
53 }
54 
55 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags)
56 {
57  int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
58  uint32_t bits[256];
59  int16_t lens[256];
60  uint8_t xlat[256];
61  int pos = 0;
62 
63  get_tree_codes(bits, lens, xlat, nodes, head, 0, 0, &pos, no_zero_count);
64  return ff_init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
65 }
66 
67 
72 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
73  Node *nodes, HuffCmp cmp, int flags)
74 {
75  int i, j;
76  int cur_node;
77  int64_t sum = 0;
78 
79  for(i = 0; i < nb_codes; i++){
80  nodes[i].sym = i;
81  nodes[i].n0 = -2;
82  sum += nodes[i].count;
83  }
84 
85  if(sum >> 31) {
86  av_log(avctx, AV_LOG_ERROR, "Too high symbol frequencies. Tree construction is not possible\n");
87  return -1;
88  }
89  qsort(nodes, nb_codes, sizeof(Node), cmp);
90  cur_node = nb_codes;
91  nodes[nb_codes*2-1].count = 0;
92  for(i = 0; i < nb_codes*2-1; i += 2){
93  nodes[cur_node].sym = HNODE;
94  nodes[cur_node].count = nodes[i].count + nodes[i+1].count;
95  nodes[cur_node].n0 = i;
96  for(j = cur_node; j > 0; j--){
97  if(nodes[j].count > nodes[j-1].count ||
98  (nodes[j].count == nodes[j-1].count &&
99  (!(flags & FF_HUFFMAN_FLAG_HNODE_FIRST) ||
100  nodes[j].n0==j-1 || nodes[j].n0==j-2 ||
101  (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
102  break;
103  FFSWAP(Node, nodes[j], nodes[j-1]);
104  }
105  cur_node++;
106  }
107  if(build_huff_tree(vlc, nodes, nb_codes*2-2, flags) < 0){
108  av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
109  return -1;
110  }
111  return 0;
112 }