FFmpeg
mjpegdec_common.c
Go to the documentation of this file.
1 /*
2  * MJPEG decoder VLC code
3  * Copyright (c) 2000, 2001 Fabrice Bellard
4  * Copyright (c) 2003 Alex Beregszaszi
5  * Copyright (c) 2003-2004 Michael Niedermayer
6  *
7  * This file is part of FFmpeg.
8  *
9  * FFmpeg is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU Lesser General Public
11  * License as published by the Free Software Foundation; either
12  * version 2.1 of the License, or (at your option) any later version.
13  *
14  * FFmpeg is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with FFmpeg; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
24 #include <stdint.h>
25 #include "libavutil/avassert.h"
26 #include "mjpegdec.h"
27 #include "vlc.h"
28 
29 static int build_huffman_codes(uint8_t *huff_size, const uint8_t *bits_table)
30 {
31  int nb_codes = 0;
32  for (int i = 1, j = 0; i <= 16; i++) {
33  nb_codes += bits_table[i];
34  av_assert1(nb_codes <= 256);
35  for (; j < nb_codes; j++)
36  huff_size[j] = i;
37  }
38  return nb_codes;
39 }
40 
41 int ff_mjpeg_build_vlc(VLC *vlc, const uint8_t *bits_table,
42  const uint8_t *val_table, int is_ac, void *logctx)
43 {
44  uint8_t huff_size[256];
45  uint16_t huff_sym[256];
46  int nb_codes = build_huffman_codes(huff_size, bits_table);
47 
48  for (int i = 0; i < nb_codes; i++) {
49  huff_sym[i] = val_table[i] + 16 * is_ac;
50 
51  if (is_ac && !val_table[i])
52  huff_sym[i] = 16 * 256;
53  }
54 
55  return ff_init_vlc_from_lengths(vlc, 9, nb_codes, huff_size, 1,
56  huff_sym, 2, 2, 0, 0, logctx);
57 }
mjpegdec.h
ff_init_vlc_from_lengths
int ff_init_vlc_from_lengths(VLC *vlc_arg, int nb_bits, int nb_codes, const int8_t *lens, int lens_wrap, const void *symbols, int symbols_wrap, int symbols_size, int offset, int flags, void *logctx)
Build VLC decoding tables suitable for use with get_vlc2()
Definition: bitstream.c:381
avassert.h
ff_mjpeg_build_vlc
int ff_mjpeg_build_vlc(VLC *vlc, const uint8_t *bits_table, const uint8_t *val_table, int is_ac, void *logctx)
Definition: mjpegdec_common.c:41
i
int i
Definition: input.c:406
av_assert1
#define av_assert1(cond)
assert() equivalent, that does not lie in speed critical code.
Definition: avassert.h:53
VLC
Definition: vlc.h:26
build_huffman_codes
static int build_huffman_codes(uint8_t *huff_size, const uint8_t *bits_table)
Definition: mjpegdec_common.c:29
vlc.h