/* * Copyright (c) 2006 Konstantin Shishkov * Copyright (c) 2007 Loren Merritt * * 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 */ /** * @file * huffman tree builder and VLC generator */ #include <stdint.h> #include "avcodec.h" #include "get_bits.h" #include "huffman.h" /* symbol for Huffman tree node */ #define HNODE -1 typedef struct { uint64_t val; int name; } HeapElem; static void heap_sift(HeapElem *h, int root, int size) { while (root * 2 + 1 < size) { int child = root * 2 + 1; if (child < size - 1 && h[child].val > h[child+1].val) child++; if (h[root].val > h[child].val) { FFSWAP(HeapElem, h[root], h[child]); root = child; } else break; } } void ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats) { HeapElem h[256]; int up[2*256]; int len[2*256]; int offset, i, next; int size = 256; for (offset = 1; ; offset <<= 1) { for (i=0; i < size; i++) { h[i].name = i; h[i].val = (stats[i] << 8) + offset; } for (i = size / 2 - 1; i >= 0; i--) heap_sift(h, i, size); for (next = size; next < size * 2 - 1; next++) { // merge the two smallest entries, and put it back in the heap uint64_t min1v = h[0].val; up[h[0].name] = next; h[0].val = INT64_MAX; heap_sift(h, 0, size); up[h[0].name] = next; h[0].name = next; h[0].val += min1v; heap_sift(h, 0, size); } len[2 * size - 2] = 0; for (i = 2 * size - 3; i >= size; i--) len[i] = len[up[i]] + 1; for (i = 0; i < size; i++) { dst[i] = len[up[i]] + 1; if (dst[i] >= 32) break; } if (i==size) break; } } 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) { int s; s = nodes[node].sym; if (s != HNODE || (no_zero_count && !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, no_zero_count); pfx |= 1; get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl, pos, no_zero_count); } } static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags, int nb_bits) { int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT); 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, no_zero_count); return ff_init_vlc_sparse(vlc, nb_bits, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0); } /** * nodes size must be 2*nb_codes * first nb_codes nodes.count must be set */ int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes, int nb_bits, Node *nodes, HuffCmp cmp, int flags) { 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; nodes[nb_codes*2-1].count = 0; for (i = 0; i < nb_codes * 2 - 1; i += 2) { uint32_t cur_count = nodes[i].count + nodes[i+1].count; // find correct place to insert new node, and // make space for the new node while at it for(j = cur_node; j > i + 2; j--){ if(cur_count > nodes[j-1].count || (cur_count == nodes[j-1].count && !(flags & FF_HUFFMAN_FLAG_HNODE_FIRST))) break; nodes[j] = nodes[j - 1]; } nodes[j].sym = HNODE; nodes[j].count = cur_count; nodes[j].n0 = i; cur_node++; } if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags, nb_bits) < 0) { av_log(avctx, AV_LOG_ERROR, "Error building tree\n"); return -1; } return 0; }