libavcodec/huffman.c

   1 /**
   2  * @file libavcodec/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 "get_bits.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, HuffCmp 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 }