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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 <stdint.h>
28 
29 #include "libavutil/qsort.h"
30 #include "libavutil/common.h"
31 
32 #include "avcodec.h"
33 #include "huffman.h"
34 #include "vlc.h"
35 
36 /* symbol for Huffman tree node */
37 #define HNODE -1
38 
39 typedef struct HeapElem {
40     uint64_t val;
41     int name;
42 } HeapElem;
43 
heap_sift(HeapElem * h,int root,int size)44 static void heap_sift(HeapElem *h, int root, int size)
45 {
46     while (root * 2 + 1 < size) {
47         int child = root * 2 + 1;
48         if (child < size - 1 && h[child].val > h[child+1].val)
49             child++;
50         if (h[root].val > h[child].val) {
51             FFSWAP(HeapElem, h[root], h[child]);
52             root = child;
53         } else
54             break;
55     }
56 }
57 
ff_huff_gen_len_table(uint8_t * dst,const uint64_t * stats,int stats_size,int skip0)58 int ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats, int stats_size, int skip0)
59 {
60     HeapElem *h  = av_malloc_array(sizeof(*h), stats_size);
61     int *up      = av_malloc_array(sizeof(*up) * 2, stats_size);
62     uint8_t *len = av_malloc_array(sizeof(*len) * 2, stats_size);
63     uint16_t *map= av_malloc_array(sizeof(*map), stats_size);
64     int offset, i, next;
65     int size = 0;
66     int ret = 0;
67 
68     if (!h || !up || !len || !map) {
69         ret = AVERROR(ENOMEM);
70         goto end;
71     }
72 
73     for (i = 0; i<stats_size; i++) {
74         dst[i] = 255;
75         if (stats[i] || !skip0)
76             map[size++] = i;
77     }
78 
79     for (offset = 1; ; offset <<= 1) {
80         for (i=0; i < size; i++) {
81             h[i].name = i;
82             h[i].val = (stats[map[i]] << 14) + offset;
83         }
84         for (i = size / 2 - 1; i >= 0; i--)
85             heap_sift(h, i, size);
86 
87         for (next = size; next < size * 2 - 1; next++) {
88             // merge the two smallest entries, and put it back in the heap
89             uint64_t min1v = h[0].val;
90             up[h[0].name] = next;
91             h[0].val = INT64_MAX;
92             heap_sift(h, 0, size);
93             up[h[0].name] = next;
94             h[0].name = next;
95             h[0].val += min1v;
96             heap_sift(h, 0, size);
97         }
98 
99         len[2 * size - 2] = 0;
100         for (i = 2 * size - 3; i >= size; i--)
101             len[i] = len[up[i]] + 1;
102         for (i = 0; i < size; i++) {
103             dst[map[i]] = len[up[i]] + 1;
104             if (dst[map[i]] >= 32) break;
105         }
106         if (i==size) break;
107     }
108 end:
109     av_free(h);
110     av_free(up);
111     av_free(len);
112     av_free(map);
113     return ret;
114 }
115 
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)116 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
117                            Node *nodes, int node,
118                            uint32_t pfx, int pl, int *pos, int no_zero_count)
119 {
120     int s;
121 
122     s = nodes[node].sym;
123     if (s != HNODE || (no_zero_count && !nodes[node].count)) {
124         bits[*pos] = pfx;
125         lens[*pos] = pl;
126         xlat[*pos] = s;
127         (*pos)++;
128     } else {
129         pfx <<= 1;
130         pl++;
131         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
132                        pos, no_zero_count);
133         pfx |= 1;
134         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
135                        pos, no_zero_count);
136     }
137 }
138 
build_huff_tree(VLC * vlc,Node * nodes,int head,int flags,int nb_bits)139 static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags, int nb_bits)
140 {
141     int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
142     uint32_t bits[256];
143     int16_t lens[256];
144     uint8_t xlat[256];
145     int pos = 0;
146 
147     get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
148                    &pos, no_zero_count);
149     return ff_init_vlc_sparse(vlc, nb_bits, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);
150 }
151 
152 
153 /**
154  * nodes size must be 2*nb_codes
155  * first nb_codes nodes.count must be set
156  */
ff_huff_build_tree(AVCodecContext * avctx,VLC * vlc,int nb_codes,int nb_bits,Node * nodes,HuffCmp cmp,int flags)157 int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes, int nb_bits,
158                        Node *nodes, HuffCmp cmp, int flags)
159 {
160     int i, j;
161     int cur_node;
162     int64_t sum = 0;
163 
164     for (i = 0; i < nb_codes; i++) {
165         nodes[i].sym = i;
166         nodes[i].n0 = -2;
167         sum += nodes[i].count;
168     }
169 
170     if (sum >> 31) {
171         av_log(avctx, AV_LOG_ERROR,
172                "Too high symbol frequencies. "
173                "Tree construction is not possible\n");
174         return -1;
175     }
176     AV_QSORT(nodes, nb_codes, Node, cmp);
177     cur_node = nb_codes;
178     nodes[nb_codes*2-1].count = 0;
179     for (i = 0; i < nb_codes * 2 - 1; i += 2) {
180         uint32_t cur_count = nodes[i].count + nodes[i+1].count;
181         // find correct place to insert new node, and
182         // make space for the new node while at it
183         for(j = cur_node; j > i + 2; j--){
184             if(cur_count > nodes[j-1].count ||
185                (cur_count == nodes[j-1].count &&
186                 !(flags & FF_HUFFMAN_FLAG_HNODE_FIRST)))
187                 break;
188             nodes[j] = nodes[j - 1];
189         }
190         nodes[j].sym = HNODE;
191         nodes[j].count = cur_count;
192         nodes[j].n0 = i;
193         cur_node++;
194     }
195     if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags, nb_bits) < 0) {
196         av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
197         return -1;
198     }
199     return 0;
200 }
201