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ffmpeg / libavcodec / huffman.c @ 2912e87a

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