FFmpeg  4.0
rangecoder.c
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1 /*
2  * Range coder
3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
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  * Range coder.
25  * based upon
26  * "Range encoding: an algorithm for removing redundancy from a digitised
27  * message.
28  * G. N. N. Martin Presented in March 1979 to the Video &
29  * Data Recording Conference,
30  * IBM UK Scientific Center held in Southampton July 24-27 1979."
31  */
32 
33 #include <string.h>
34 
35 #include "libavutil/attributes.h"
36 #include "libavutil/avassert.h"
37 #include "libavutil/intreadwrite.h"
38 
39 #include "avcodec.h"
40 #include "rangecoder.h"
41 
43 {
44  c->bytestream_start =
45  c->bytestream = buf;
46  c->bytestream_end = buf + buf_size;
47  c->low = 0;
48  c->range = 0xFF00;
49  c->outstanding_count = 0;
50  c->outstanding_byte = -1;
51 }
52 
54  int buf_size)
55 {
56  /* cast to avoid compiler warning */
57  ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
58 
59  c->low = AV_RB16(c->bytestream);
60  c->bytestream += 2;
61  c->overread = 0;
62  if (c->low >= 0xFF00) {
63  c->low = 0xFF00;
64  c->bytestream_end = c->bytestream;
65  }
66 }
67 
68 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
69 {
70  const int64_t one = 1LL << 32;
71  int64_t p;
72  int last_p8, p8, i;
73 
74  memset(c->zero_state, 0, sizeof(c->zero_state));
75  memset(c->one_state, 0, sizeof(c->one_state));
76 
77  last_p8 = 0;
78  p = one / 2;
79  for (i = 0; i < 128; i++) {
80  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
81  if (p8 <= last_p8)
82  p8 = last_p8 + 1;
83  if (last_p8 && last_p8 < 256 && p8 <= max_p)
84  c->one_state[last_p8] = p8;
85 
86  p += ((one - p) * factor + one / 2) >> 32;
87  last_p8 = p8;
88  }
89 
90  for (i = 256 - max_p; i <= max_p; i++) {
91  if (c->one_state[i])
92  continue;
93 
94  p = (i * one + 128) >> 8;
95  p += ((one - p) * factor + one / 2) >> 32;
96  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
97  if (p8 <= i)
98  p8 = i + 1;
99  if (p8 > max_p)
100  p8 = max_p;
101  c->one_state[i] = p8;
102  }
103 
104  for (i = 1; i < 255; i++)
105  c->zero_state[i] = 256 - c->one_state[256 - i];
106 }
107 
108 /* Return the number of bytes written. */
110 {
111  c->range = 0xFF;
112  c->low += 0xFF;
113  renorm_encoder(c);
114  c->range = 0xFF;
115  renorm_encoder(c);
116 
117  av_assert1(c->low == 0);
118  av_assert1(c->range >= 0x100);
119 
120  return c->bytestream - c->bytestream_start;
121 }
uint32_t low
Definition: mss3.c:64
uint8_t zero_state[256]
Definition: rangecoder.h:40
Range coder.
uint8_t * bytestream_end
Definition: rangecoder.h:44
uint32_t range
Definition: mss3.c:64
uint8_t one_state[256]
Definition: rangecoder.h:41
Macro definitions for various function/variable attributes.
int ff_rac_terminate(RangeCoder *c)
Definition: rangecoder.c:109
uint8_t
#define av_cold
Definition: attributes.h:82
#define AV_RB16
Definition: intreadwrite.h:53
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:54
simple assert() macros that are a bit more flexible than ISO C assert().
uint8_t * bytestream
Definition: rangecoder.h:43
#define av_assert1(cond)
assert() equivalent, that does not lie in speed critical code.
Definition: avassert.h:53
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
Definition: rangecoder.c:68
int outstanding_byte
Definition: rangecoder.h:39
Libavcodec external API header.
void * buf
Definition: avisynth_c.h:690
av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
Definition: rangecoder.c:42
av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:53
static const int factor[16]
Definition: vf_pp7.c:75
int overread
Definition: rangecoder.h:45
static double c[64]
int outstanding_count
Definition: rangecoder.h:38
uint8_t * bytestream_start
Definition: rangecoder.h:42