1/*
2 * Mersenne Twister PRNG algorithm
3 * Copyright (c) 2006 Ryan Martell
4 * Based on a C program for MT19937, with initialization improved 2002/1/26.
5 * Coded by 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 "avutil.h"
30#include "common.h"
31
32typedef struct {
33    unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
34    int index; ///< Current untempered value we use as the base.
35} AVRandomState;
36
37
38#if LIBAVUTIL_VERSION_MAJOR < 50
39attribute_deprecated void av_init_random(unsigned int seed, AVRandomState *state);
40#endif
41void 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.
42void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop).
43
44/**
45 * Generates a random number from the interval [0,0xffffffff].
46 *
47 * Please do NOT use the Mersenne Twister, it is slow. Use the random number
48 * generator from lfg.c/h or a simple LCG like state = state*1664525+1013904223.
49 * If you still choose to use MT, expect that you will have to provide
50 * some evidence that it makes a difference for the case where you use it.
51 */
52static inline unsigned int av_random(AVRandomState *state)
53{
54    unsigned int y;
55
56    // Regenerate the untempered numbers if we should...
57    if (state->index >= AV_RANDOM_N)
58        av_random_generate_untempered_numbers(state);
59
60    // Grab one...
61    y = state->mt[state->index++];
62
63    /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937 are.. */
64    y ^= (y >> 11);
65    y ^= (y << 7) & 0x9d2c5680;
66    y ^= (y << 15) & 0xefc60000;
67    y ^= (y >> 18);
68
69    return y;
70}
71
72/** Returns a random number in the range [0-1] as double. */
73static inline double av_random_real1(AVRandomState *state)
74{
75    /* divided by 2^32-1 */
76    return av_random(state) * (1.0 / 4294967296.0);
77}
78
79#endif /* AVUTIL_RANDOM_H */
80