libavcodec/huffman.c

   1 /*
   2  * Copyright (c) 2006 Konstantin Shishkov
   3  * Copyright (c) 2007 Loren Merritt
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * huffman tree builder and VLC generator
  25  */
  26
  27 #include <stdint.h>
  28
  29 #include "libavutil/error.h"
  30 #include "libavutil/log.h"
  31 #include "libavutil/macros.h"
  32 #include "libavutil/mem.h"
  33 #include "libavutil/qsort.h"
  34
  35 #include "huffman.h"
  36 #include "vlc.h"
  37
  38 /* symbol for Huffman tree node */
  39 #define HNODE -1
  40
  41 typedef struct HeapElem {
  42     uint64_t val;
  43     int name;
  44 } HeapElem;
  45
  46 static void heap_sift(HeapElem *h, int root, int size)
  47 {
  48     while (root * 2 + 1 < size) {
  49         int child = root * 2 + 1;
  50         if (child < size - 1 && h[child].val > h[child+1].val)
  51             child++;
  52         if (h[root].val > h[child].val) {
  53             FFSWAP(HeapElem, h[root], h[child]);
  54             root = child;
  55         } else
  56             break;
  57     }
  58 }
  59
  60 int ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats, int stats_size, int skip0)
  61 {
  62     HeapElem *h  = av_malloc_array(sizeof(*h), stats_size);
  63     int *up      = av_malloc_array(sizeof(*up) * 2, stats_size);
  64     uint8_t *len = av_malloc_array(sizeof(*len) * 2, stats_size);
  65     uint16_t *map= av_malloc_array(sizeof(*map), stats_size);
  66     int offset, i, next;
  67     int size = 0;
  68     int ret = 0;
  69
  70     if (!h || !up || !len || !map) {
  71         ret = AVERROR(ENOMEM);
  72         goto end;
  73     }
  74
  75     for (i = 0; i<stats_size; i++) {
  76         dst[i] = 255;
  77         if (stats[i] || !skip0)
  78             map[size++] = i;
  79     }
  80
  81     for (offset = 1; ; offset <<= 1) {
  82         for (i=0; i < size; i++) {
  83             h[i].name = i;
  84             h[i].val = (stats[map[i]] << 14) + offset;
  85         }
  86         for (i = size / 2 - 1; i >= 0; i--)
  87             heap_sift(h, i, size);
  88
  89         for (next = size; next < size * 2 - 1; next++) {
  90             // merge the two smallest entries, and put it back in the heap
  91             uint64_t min1v = h[0].val;
  92             up[h[0].name] = next;
  93             h[0].val = INT64_MAX;
  94             heap_sift(h, 0, size);
  95             up[h[0].name] = next;
  96             h[0].name = next;
  97             h[0].val += min1v;
  98             heap_sift(h, 0, size);
  99         }
 100
 101         len[2 * size - 2] = 0;
 102         for (i = 2 * size - 3; i >= size; i--)
 103             len[i] = len[up[i]] + 1;
 104         for (i = 0; i < size; i++) {
 105             dst[map[i]] = len[up[i]] + 1;
 106             if (dst[map[i]] >= 32) break;
 107         }
 108         if (i==size) break;
 109     }
 110 end:
 111     av_free(h);
 112     av_free(up);
 113     av_free(len);
 114     av_free(map);
 115     return ret;
 116 }
 117
 118 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
 119                            Node *nodes, int node,
 120                            uint32_t pfx, int pl, int *pos, int no_zero_count)
 121 {
 122     int s;
 123
 124     s = nodes[node].sym;
 125     if (s != HNODE || (no_zero_count && !nodes[node].count)) {
 126         bits[*pos] = pfx;
 127         lens[*pos] = pl;
 128         xlat[*pos] = s;
 129         (*pos)++;
 130     } else {
 131         pfx <<= 1;
 132         pl++;
 133         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
 134                        pos, no_zero_count);
 135         pfx |= 1;
 136         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
 137                        pos, no_zero_count);
 138     }
 139 }
 140
 141 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags, int nb_bits)
 142 {
 143     int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
 144     uint32_t bits[256];
 145     int16_t lens[256];
 146     uint8_t xlat[256];
 147     int pos = 0;
 148
 149     get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
 150                    &pos, no_zero_count);
 151     return ff_vlc_init_sparse(vlc, nb_bits, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
 152 }
 153
 154
 155 /**
 156  * nodes size must be 2*nb_codes
 157  * first nb_codes nodes.count must be set
 158  */
 159 int ff_huff_build_tree(void *logctx, VLC *vlc, int nb_codes, int nb_bits,
 160                        Node *nodes, HuffCmp cmp, int flags)
 161 {
 162     int i, j;
 163     int cur_node;
 164     int64_t sum = 0;
 165
 166     for (i = 0; i < nb_codes; i++) {
 167         nodes[i].sym = i;
 168         nodes[i].n0 = -2;
 169         sum += nodes[i].count;
 170     }
 171
 172     if (sum >> 31) {
 173         av_log(logctx, AV_LOG_ERROR,
 174                "Too high symbol frequencies. "
 175                "Tree construction is not possible\n");
 176         return -1;
 177     }
 178     AV_QSORT(nodes, nb_codes, Node, cmp);
 179     cur_node = nb_codes;
 180     nodes[nb_codes*2-1].count = 0;
 181     for (i = 0; i < nb_codes * 2 - 1; i += 2) {
 182         uint32_t cur_count = nodes[i].count + nodes[i+1].count;
 183         // find correct place to insert new node, and
 184         // make space for the new node while at it
 185         for(j = cur_node; j > i + 2; j--){
 186             if(cur_count > nodes[j-1].count ||
 187                (cur_count == nodes[j-1].count &&
 188                 !(flags & FF_HUFFMAN_FLAG_HNODE_FIRST)))
 189                 break;
 190             nodes[j] = nodes[j - 1];
 191         }
 192         nodes[j].sym = HNODE;
 193         nodes[j].count = cur_count;
 194         nodes[j].n0 = i;
 195         cur_node++;
 196     }
 197     if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags, nb_bits) < 0) {
 198         av_log(logctx, AV_LOG_ERROR, "Error building tree\n");
 199         return -1;
 200     }
 201     return 0;
 202 }