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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 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 "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, FF_HUFFMAN_BITS, 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  uint32_t cur_count = nodes[i].count + nodes[i+1].count;
157  // find correct place to insert new node, and
158  // make space for the new node while at it
159  for(j = cur_node; j > i + 2; j--){
160  if(cur_count > nodes[j-1].count ||
161  (cur_count == nodes[j-1].count &&
162  !(flags & FF_HUFFMAN_FLAG_HNODE_FIRST)))
163  break;
164  nodes[j] = nodes[j - 1];
165  }
166  nodes[j].sym = HNODE;
167  nodes[j].count = cur_count;
168  nodes[j].n0 = i;
169  cur_node++;
170  }
171  if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags) < 0) {
172  av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
173  return -1;
174  }
175  return 0;
176 }