Deprecate av_init_random() in favour of av_random_init(), with a more natural
[libav.git] / libavutil / random.h
1 /*
2 * Mersenne Twister Random Algorithm
3 * Copyright (c) 2006 Ryan Martell.
4 * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
5 * Takuji Nishimura and Makoto Matsumoto.
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 #ifndef AVUTIL_RANDOM_H
25 #define AVUTIL_RANDOM_H
26
27 #define AV_RANDOM_N 624
28
29 #include "common.h"
30
31 typedef struct {
32 unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
33 int index; ///< Current untempered value we use as the base.
34 } AVRandomState;
35
36
37 attribute_deprecated void av_init_random(unsigned int seed, AVRandomState *state);
38 void av_random_init(AVRandomState *state, unsigned int seed); ///< To be inlined, the struct must be visible. So it does not make sense to try and keep it opaque with malloc/free-like calls.
39 void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop).
40
41 /**
42 * Generates a random number from the interval [0,0xffffffff].
43 *
44 * Please do NOT use the Mersenne Twister, it is slow. Use the random generator
45 * from lfg.c/h or a simple LCG like state= state*1664525+1013904223.
46 * If you still choose to use MT, expect that you will have to provide
47 * some evidence that it makes a difference for the case where you use it.
48 */
49 static inline unsigned int av_random(AVRandomState *state)
50 {
51 unsigned int y;
52
53 // Regenerate the untempered numbers if we should...
54 if (state->index >= AV_RANDOM_N)
55 av_random_generate_untempered_numbers(state);
56
57 // Grab one...
58 y = state->mt[state->index++];
59
60 /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937 are.. */
61 y ^= (y >> 11);
62 y ^= (y << 7) & 0x9d2c5680;
63 y ^= (y << 15) & 0xefc60000;
64 y ^= (y >> 18);
65
66 return y;
67 }
68
69 /** Return random in range [0-1] as double. */
70 static inline double av_random_real1(AVRandomState *state)
71 {
72 /* divided by 2^32-1 */
73 return av_random(state) * (1.0 / 4294967296.0);
74 }
75
76 #endif /* AVUTIL_RANDOM_H */