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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 | ||
34 | #include <string.h> | |
35 | ||
36 | #include "libavutil/attributes.h" | |
37 | #include "libavutil/avassert.h" | |
38 | #include "avcodec.h" | |
39 | #include "rangecoder.h" | |
40 | #include "bytestream.h" | |
41 | ||
42 | av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size) | |
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 | ||
53 | av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, | |
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 = bytestream_get_be16((const uint8_t **)&c->bytestream); | |
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. */ | |
103 | int ff_rac_terminate(RangeCoder *c) | |
104 | { | |
105 | c->range = 0xFF; | |
106 | c->low += 0xFF; | |
107 | renorm_encoder(c); | |
108 | c->range = 0xFF; | |
109 | renorm_encoder(c); | |
110 | ||
111 | av_assert1(c->low == 0); | |
112 | av_assert1(c->range >= 0x100); | |
113 | ||
114 | return c->bytestream - c->bytestream_start; | |
115 | } | |
116 | ||
117 | #ifdef TEST | |
118 | #define SIZE 10240 | |
119 | ||
120 | #include "libavutil/lfg.h" | |
121 | #include "libavutil/log.h" | |
122 | ||
123 | static uint8_t b[9 * SIZE]; | |
124 | static uint8_t r[9 * SIZE]; | |
125 | ||
126 | int main(void) | |
127 | { | |
128 | RangeCoder c; | |
129 | int i; | |
130 | uint8_t state[10]; | |
131 | AVLFG prng; | |
132 | ||
133 | av_lfg_init(&prng, 1); | |
134 | ||
135 | ff_init_range_encoder(&c, b, SIZE); | |
136 | ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16); | |
137 | ||
138 | memset(state, 128, sizeof(state)); | |
139 | ||
140 | for (i = 0; i < SIZE; i++) | |
141 | r[i] = av_lfg_get(&prng) % 7; | |
142 | ||
143 | for (i = 0; i < SIZE; i++) | |
144 | put_rac(&c, state, r[i] & 1); | |
145 | ||
146 | ff_rac_terminate(&c); | |
147 | ||
148 | ff_init_range_decoder(&c, b, SIZE); | |
149 | ||
150 | memset(state, 128, sizeof(state)); | |
151 | ||
152 | for (i = 0; i < SIZE; i++) | |
153 | if ((r[i] & 1) != get_rac(&c, state)) { | |
154 | av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i); | |
155 | return 1; | |
156 | } | |
157 | ||
158 | return 0; | |
159 | } | |
160 | #endif /* TEST */ |