Libav
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 Libav.
6  *
7  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
33 #include <string.h>
34 
35 #include "libavutil/attributes.h"
36 #include "libavutil/intreadwrite.h"
37 
38 #include "avcodec.h"
39 #include "rangecoder.h"
40 
41 av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
42 {
43  c->bytestream_start =
44  c->bytestream = buf;
45  c->bytestream_end = buf + buf_size;
46  c->low = 0;
47  c->range = 0xFF00;
48  c->outstanding_count = 0;
49  c->outstanding_byte = -1;
50 }
51 
53  int buf_size)
54 {
55  /* cast to avoid compiler warning */
56  ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
57 
58  c->low = AV_RB16(c->bytestream);
59  c->bytestream += 2;
60 }
61 
62 void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
63 {
64  const int64_t one = 1LL << 32;
65  int64_t p;
66  int last_p8, p8, i;
67 
68  memset(c->zero_state, 0, sizeof(c->zero_state));
69  memset(c->one_state, 0, sizeof(c->one_state));
70 
71  last_p8 = 0;
72  p = one / 2;
73  for (i = 0; i < 128; i++) {
74  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
75  if (p8 <= last_p8)
76  p8 = last_p8 + 1;
77  if (last_p8 && last_p8 < 256 && p8 <= max_p)
78  c->one_state[last_p8] = p8;
79 
80  p += ((one - p) * factor + one / 2) >> 32;
81  last_p8 = p8;
82  }
83 
84  for (i = 256 - max_p; i <= max_p; i++) {
85  if (c->one_state[i])
86  continue;
87 
88  p = (i * one + 128) >> 8;
89  p += ((one - p) * factor + one / 2) >> 32;
90  p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
91  if (p8 <= i)
92  p8 = i + 1;
93  if (p8 > max_p)
94  p8 = max_p;
95  c->one_state[i] = p8;
96  }
97 
98  for (i = 1; i < 255; i++)
99  c->zero_state[i] = 256 - c->one_state[256 - i];
100 }
101 
102 /* Return the number of bytes written. */
104 {
105  c->range = 0xFF;
106  c->low += 0xFF;
107  renorm_encoder(c);
108  c->range = 0xFF;
109  renorm_encoder(c);
110 
111  assert(c->low == 0);
112  assert(c->range >= 0x100);
113 
114  return c->bytestream - c->bytestream_start;
115 }
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:103
uint8_t
#define av_cold
Definition: attributes.h:66
#define AV_RB16
Definition: intreadwrite.h:53
static void renorm_encoder(RangeCoder *c)
Definition: rangecoder.h:52
uint8_t * bytestream
Definition: rangecoder.h:43
void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
Definition: rangecoder.c:62
int outstanding_byte
Definition: rangecoder.h:39
Libavcodec external API header.
av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
Definition: rangecoder.c:41
av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
Definition: rangecoder.c:52
int outstanding_count
Definition: rangecoder.h:38
uint8_t * bytestream_start
Definition: rangecoder.h:42