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/**
* @file huffman.c
* huffman tree builder and VLC generator
* Copyright (c) 2006 Konstantin Shishkov
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "avcodec.h"
#include "bitstream.h"
#include "huffman.h"
/* symbol for Huffman tree node */
#define HNODE -1
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 s;
s = nodes[node].sym;
if(s != HNODE || !nodes[node].count){
bits[*pos] = pfx;
lens[*pos] = pl;
xlat[*pos] = s;
(*pos)++;
}else{
pfx <<= 1;
pl++;
get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl, pos);
pfx |= 1;
get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0+1, pfx, pl, pos);
}
}
static int build_huff_tree(VLC *vlc, Node *nodes, int head)
{
uint32_t bits[256];
int16_t lens[256];
uint8_t xlat[256];
int pos = 0;
get_tree_codes(bits, lens, xlat, nodes, head, 0, 0, &pos);
return init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
}
/**
* first nb_codes nodes.count must be set
*/
int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
Node nodes[2*nb_codes], huff_cmp_t cmp, int hnode_first)
{
int i, j;
int cur_node;
int64_t sum = 0;
for(i = 0; i < nb_codes; i++){
nodes[i].sym = i;
nodes[i].n0 = -2;
sum += nodes[i].count;
}
if(sum >> 31) {
av_log(avctx, AV_LOG_ERROR, "Too high symbol frequencies. Tree construction is not possible\n");
return -1;
}
qsort(nodes, nb_codes, sizeof(Node), cmp);
cur_node = nb_codes;
for(i = 0; i < nb_codes*2-1; i += 2){
nodes[cur_node].sym = HNODE;
nodes[cur_node].count = nodes[i].count + nodes[i+1].count;
nodes[cur_node].n0 = i;
for(j = cur_node; j > 0; j--){
if(nodes[j].count > nodes[j-1].count ||
(nodes[j].count == nodes[j-1].count &&
(!hnode_first || nodes[j].n0==j-1 || nodes[j].n0==j-2 ||
(nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
break;
FFSWAP(Node, nodes[j], nodes[j-1]);
}
cur_node++;
}
if(build_huff_tree(vlc, nodes, nb_codes*2-2) < 0){
av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
return -1;
}
return 0;
}
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