libavcodec/huffman.c

   1 /*
   2  * Copyright (c) 2006 Konstantin Shishkov
   3  * Copyright (c) 2007 Loren Merritt
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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 "avcodec.h"
  28 #include "get_bits.h"
  29 #include "huffman.h"
  30
  31 /* symbol for Huffman tree node */
  32 #define HNODE -1
  33
  34 typedef struct {
  35     uint64_t val;
  36     int name;
  37 } HeapElem;
  38
  39 static void heap_sift(HeapElem *h, int root, int size)
  40 {
  41     while (root * 2 + 1 < size) {
  42         int child = root * 2 + 1;
  43         if (child < size - 1 && h[child].val > h[child+1].val)
  44             child++;
  45         if (h[root].val > h[child].val) {
  46             FFSWAP(HeapElem, h[root], h[child]);
  47             root = child;
  48         } else
  49             break;
  50     }
  51 }
  52
  53 void ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats)
  54 {
  55     HeapElem h[256];
  56     int up[2*256];
  57     int len[2*256];
  58     int offset, i, next;
  59     int size = 256;
  60
  61     for (offset = 1; ; offset <<= 1) {
  62         for (i=0; i < size; i++) {
  63             h[i].name = i;
  64             h[i].val = (stats[i] << 8) + offset;
  65         }
  66         for (i = size / 2 - 1; i >= 0; i--)
  67             heap_sift(h, i, size);
  68
  69         for (next = size; next < size * 2 - 1; next++) {
  70             // merge the two smallest entries, and put it back in the heap
  71             uint64_t min1v = h[0].val;
  72             up[h[0].name] = next;
  73             h[0].val = INT64_MAX;
  74             heap_sift(h, 0, size);
  75             up[h[0].name] = next;
  76             h[0].name = next;
  77             h[0].val += min1v;
  78             heap_sift(h, 0, size);
  79         }
  80
  81         len[2 * size - 2] = 0;
  82         for (i = 2 * size - 3; i >= size; i--)
  83             len[i] = len[up[i]] + 1;
  84         for (i = 0; i < size; i++) {
  85             dst[i] = len[up[i]] + 1;
  86             if (dst[i] >= 32) break;
  87         }
  88         if (i==size) break;
  89     }
  90 }
  91
  92 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
  93                            Node *nodes, int node,
  94                            uint32_t pfx, int pl, int *pos, int no_zero_count)
  95 {
  96     int s;
  97
  98     s = nodes[node].sym;
  99     if (s != HNODE || (no_zero_count && !nodes[node].count)) {
 100         bits[*pos] = pfx;
 101         lens[*pos] = pl;
 102         xlat[*pos] = s;
 103         (*pos)++;
 104     } else {
 105         pfx <<= 1;
 106         pl++;
 107         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
 108                        pos, no_zero_count);
 109         pfx |= 1;
 110         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
 111                        pos, no_zero_count);
 112     }
 113 }
 114
 115 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags)
 116 {
 117     int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
 118     uint32_t bits[256];
 119     int16_t lens[256];
 120     uint8_t xlat[256];
 121     int pos = 0;
 122
 123     get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
 124                    &pos, no_zero_count);
 125     return ff_init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
 126 }
 127
 128
 129 /**
 130  * nodes size must be 2*nb_codes
 131  * first nb_codes nodes.count must be set
 132  */
 133 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
 134                        Node *nodes, HuffCmp cmp, int flags)
 135 {
 136     int i, j;
 137     int cur_node;
 138     int64_t sum = 0;
 139
 140     for (i = 0; i < nb_codes; i++) {
 141         nodes[i].sym = i;
 142         nodes[i].n0 = -2;
 143         sum += nodes[i].count;
 144     }
 145
 146     if (sum >> 31) {
 147         av_log(avctx, AV_LOG_ERROR,
 148                "Too high symbol frequencies. "
 149                "Tree construction is not possible\n");
 150         return -1;
 151     }
 152     qsort(nodes, nb_codes, sizeof(Node), cmp);
 153     cur_node = nb_codes;
 154     nodes[nb_codes*2-1].count = 0;
 155     for (i = 0; i < nb_codes * 2 - 1; i += 2) {
 156         nodes[cur_node].sym = HNODE;
 157         nodes[cur_node].count = nodes[i].count + nodes[i + 1].count;
 158         nodes[cur_node].n0 = i;
 159         for (j = cur_node; j > 0; j--) {
 160             if (nodes[j].count > nodes[j - 1].count ||
 161                 (nodes[j].count == nodes[j - 1].count &&
 162                  (!(flags & FF_HUFFMAN_FLAG_HNODE_FIRST) ||
 163                   nodes[j].n0 == j - 1 || nodes[j].n0 == j - 2 ||
 164                   (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
 165                 break;
 166             FFSWAP(Node, nodes[j], nodes[j - 1]);
 167         }
 168         cur_node++;
 169     }
 170     if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags) < 0) {
 171         av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
 172         return -1;
 173     }
 174     return 0;
 175 }