Libav
huffman.c
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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 
27 #include <stdint.h>
28 
29 #include "avcodec.h"
30 #include "get_bits.h"
31 #include "huffman.h"
32 
33 /* symbol for Huffman tree node */
34 #define HNODE -1
35 
36 typedef struct {
37  uint64_t val;
38  int name;
39 } HeapElem;
40 
41 static void heap_sift(HeapElem *h, int root, int size)
42 {
43  while (root * 2 + 1 < size) {
44  int child = root * 2 + 1;
45  if (child < size - 1 && h[child].val > h[child+1].val)
46  child++;
47  if (h[root].val > h[child].val) {
48  FFSWAP(HeapElem, h[root], h[child]);
49  root = child;
50  } else
51  break;
52  }
53 }
54 
55 void ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats)
56 {
57  HeapElem h[256];
58  int up[2*256];
59  int len[2*256];
60  int offset, i, next;
61  int size = 256;
62 
63  for (offset = 1; ; offset <<= 1) {
64  for (i=0; i < size; i++) {
65  h[i].name = i;
66  h[i].val = (stats[i] << 8) + offset;
67  }
68  for (i = size / 2 - 1; i >= 0; i--)
69  heap_sift(h, i, size);
70 
71  for (next = size; next < size * 2 - 1; next++) {
72  // merge the two smallest entries, and put it back in the heap
73  uint64_t min1v = h[0].val;
74  up[h[0].name] = next;
75  h[0].val = INT64_MAX;
76  heap_sift(h, 0, size);
77  up[h[0].name] = next;
78  h[0].name = next;
79  h[0].val += min1v;
80  heap_sift(h, 0, size);
81  }
82 
83  len[2 * size - 2] = 0;
84  for (i = 2 * size - 3; i >= size; i--)
85  len[i] = len[up[i]] + 1;
86  for (i = 0; i < size; i++) {
87  dst[i] = len[up[i]] + 1;
88  if (dst[i] >= 32) break;
89  }
90  if (i==size) break;
91  }
92 }
93 
94 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
95  Node *nodes, int node,
96  uint32_t pfx, int pl, int *pos, int no_zero_count)
97 {
98  int s;
99 
100  s = nodes[node].sym;
101  if (s != HNODE || (no_zero_count && !nodes[node].count)) {
102  bits[*pos] = pfx;
103  lens[*pos] = pl;
104  xlat[*pos] = s;
105  (*pos)++;
106  } else {
107  pfx <<= 1;
108  pl++;
109  get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
110  pos, no_zero_count);
111  pfx |= 1;
112  get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
113  pos, no_zero_count);
114  }
115 }
116 
117 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags)
118 {
119  int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
120  uint32_t bits[256];
121  int16_t lens[256];
122  uint8_t xlat[256];
123  int pos = 0;
124 
125  get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
126  &pos, no_zero_count);
127  return ff_init_vlc_sparse(vlc, 9, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
128 }
129 
130 
135 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
136  Node *nodes, HuffCmp cmp, int flags)
137 {
138  int i, j;
139  int cur_node;
140  int64_t sum = 0;
141 
142  for (i = 0; i < nb_codes; i++) {
143  nodes[i].sym = i;
144  nodes[i].n0 = -2;
145  sum += nodes[i].count;
146  }
147 
148  if (sum >> 31) {
149  av_log(avctx, AV_LOG_ERROR,
150  "Too high symbol frequencies. "
151  "Tree construction is not possible\n");
152  return -1;
153  }
154  qsort(nodes, nb_codes, sizeof(Node), cmp);
155  cur_node = nb_codes;
156  nodes[nb_codes*2-1].count = 0;
157  for (i = 0; i < nb_codes * 2 - 1; i += 2) {
158  nodes[cur_node].sym = HNODE;
159  nodes[cur_node].count = nodes[i].count + nodes[i + 1].count;
160  nodes[cur_node].n0 = i;
161  for (j = cur_node; j > 0; j--) {
162  if (nodes[j].count > nodes[j - 1].count ||
163  (nodes[j].count == nodes[j - 1].count &&
164  (!(flags & FF_HUFFMAN_FLAG_HNODE_FIRST) ||
165  nodes[j].n0 == j - 1 || nodes[j].n0 == j - 2 ||
166  (nodes[j].sym!=HNODE && nodes[j-1].sym!=HNODE))))
167  break;
168  FFSWAP(Node, nodes[j], nodes[j - 1]);
169  }
170  cur_node++;
171  }
172  if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags) < 0) {
173  av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
174  return -1;
175  }
176  return 0;
177 }