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 */
26
27 #ifndef AVCODEC_RANGECODER_H
28 #define AVCODEC_RANGECODER_H
29
30 #include <stdint.h>
31
32 #include "libavutil/common.h"
33 #include "libavutil/avassert.h"
34
35 typedef struct RangeCoder {
36 int low;
37 int range;
38 int outstanding_count;
39 int outstanding_byte;
40 uint8_t zero_state[256];
41 uint8_t one_state[256];
42 uint8_t *bytestream_start;
43 uint8_t *bytestream;
44 uint8_t *bytestream_end;
45 int overread;
46 #define MAX_OVERREAD 2
47 } RangeCoder;
48
49 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
50 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
51
52 /**
53 * Terminates the range coder
54 * @param version version 0 requires the decoder to know the data size in bytes
55 * version 1 needs about 1 bit more space but does not need to
56 * carry the size from encoder to decoder
57 */
58 int ff_rac_terminate(RangeCoder *c, int version);
59
60 /**
61 * Check if at the current position there is a valid looking termination
62 * @param version version 0 requires the decoder to know the data size in bytes
63 * version 1 needs about 1 bit more space but does not need to
64 * carry the size from encoder to decoder
65 * @returns negative AVERROR code on error or non negative.
66 */
67 int ff_rac_check_termination(RangeCoder *c, int version);
68
69 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
70
renorm_encoder(RangeCoder * c)71 static inline void renorm_encoder(RangeCoder *c)
72 {
73 // FIXME: optimize
74 while (c->range < 0x100) {
75 if (c->outstanding_byte < 0) {
76 c->outstanding_byte = c->low >> 8;
77 } else if (c->low <= 0xFF00) {
78 *c->bytestream++ = c->outstanding_byte;
79 for (; c->outstanding_count; c->outstanding_count--)
80 *c->bytestream++ = 0xFF;
81 c->outstanding_byte = c->low >> 8;
82 } else if (c->low >= 0x10000) {
83 *c->bytestream++ = c->outstanding_byte + 1;
84 for (; c->outstanding_count; c->outstanding_count--)
85 *c->bytestream++ = 0x00;
86 c->outstanding_byte = (c->low >> 8) & 0xFF;
87 } else {
88 c->outstanding_count++;
89 }
90
91 c->low = (c->low & 0xFF) << 8;
92 c->range <<= 8;
93 }
94 }
95
get_rac_count(RangeCoder * c)96 static inline int get_rac_count(RangeCoder *c)
97 {
98 int x = c->bytestream - c->bytestream_start + c->outstanding_count;
99 if (c->outstanding_byte >= 0)
100 x++;
101 return 8 * x - av_log2(c->range);
102 }
103
put_rac(RangeCoder * c,uint8_t * const state,int bit)104 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
105 {
106 int range1 = (c->range * (*state)) >> 8;
107
108 av_assert2(*state);
109 av_assert2(range1 < c->range);
110 av_assert2(range1 > 0);
111 if (!bit) {
112 c->range -= range1;
113 *state = c->zero_state[*state];
114 } else {
115 c->low += c->range - range1;
116 c->range = range1;
117 *state = c->one_state[*state];
118 }
119
120 renorm_encoder(c);
121 }
122
refill(RangeCoder * c)123 static inline void refill(RangeCoder *c)
124 {
125 if (c->range < 0x100) {
126 c->range <<= 8;
127 c->low <<= 8;
128 if (c->bytestream < c->bytestream_end) {
129 c->low += c->bytestream[0];
130 c->bytestream++;
131 } else
132 c->overread ++;
133 }
134 }
135
get_rac(RangeCoder * c,uint8_t * const state)136 static inline int get_rac(RangeCoder *c, uint8_t *const state)
137 {
138 int range1 = (c->range * (*state)) >> 8;
139
140 c->range -= range1;
141 if (c->low < c->range) {
142 *state = c->zero_state[*state];
143 refill(c);
144 return 0;
145 } else {
146 c->low -= c->range;
147 *state = c->one_state[*state];
148 c->range = range1;
149 refill(c);
150 return 1;
151 }
152 }
153
154 #endif /* AVCODEC_RANGECODER_H */
155