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/*
* 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 "libavutil/error.h"
#include "libavutil/log.h"
#include "libavutil/macros.h"
#include "libavutil/mem.h"
#include "libavutil/qsort.h"
#include "huffman.h"
#include "vlc.h"
/* symbol for Huffman tree node */
#define HNODE -1
typedef struct HeapElem {
union {
uint64_t val;
uint16_t dummy; // exists solely to ensure alignof(HeapElem) >= alignof(uint16_t)
};
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;
}
}
int ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats, int stats_size, int skip0)
{
int *up;
uint16_t *map;
uint8_t *len;
HeapElem *h = av_malloc_array(stats_size,
sizeof(*h) + 2 * sizeof(up) + 2 * sizeof(len) + sizeof(map));
if (!h)
return AVERROR(ENOMEM);
up = (int*)(h + stats_size);
// map is suitably aligned because up uses an even number of elements
// and alignof(uint16_t) is either 1 or 2.
map = (uint16_t*)(up + 2 * stats_size);
len = (uint8_t*)(map + stats_size);
int offset, i, next;
int size = 0;
int ret = 0;
for (i = 0; i<stats_size; i++) {
dst[i] = 255;
if (stats[i] || !skip0)
map[size++] = i;
}
for (offset = 1; ; offset <<= 1) {
for (i=0; i < size; i++) {
h[i].name = i;
h[i].val = (stats[map[i]] << 14) + 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[map[i]] = len[up[i]] + 1;
if (dst[map[i]] >= 32) break;
}
if (i==size) break;
}
av_free(h);
return ret;
}
static void get_tree_codes(int8_t *lens, uint8_t *xlat,
Node *nodes, int node, int pl, int *pos, int no_zero_count)
{
int s;
s = nodes[node].sym;
if (s != HNODE || (no_zero_count && !nodes[node].count)) {
lens[*pos] = pl;
xlat[*pos] = s;
(*pos)++;
} else {
pl++;
get_tree_codes(lens, xlat, nodes, nodes[node].n0, pl,
pos, no_zero_count);
get_tree_codes(lens, xlat, nodes, nodes[node].n0 + 1, pl,
pos, no_zero_count);
}
}
static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags, int nb_bits, void *logctx)
{
int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);
int8_t lens[256];
uint8_t xlat[256];
int pos = 0;
get_tree_codes(lens, xlat, nodes, head, 0,
&pos, no_zero_count);
return ff_vlc_init_from_lengths(vlc, nb_bits, pos, lens, 1,
xlat, 1, 1, 0, 0, logctx);
}
/**
* nodes size must be 2*nb_codes
* first nb_codes nodes.count must be set
*/
int ff_huff_build_tree(void *logctx, 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(logctx, AV_LOG_ERROR,
"Too high symbol frequencies. "
"Tree construction is not possible\n");
return -1;
}
AV_QSORT(nodes, nb_codes, 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, logctx) < 0) {
av_log(logctx, AV_LOG_ERROR, "Error building tree\n");
return -1;
}
return 0;
}
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