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