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.
7 * This file is part of FFmpeg.
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.
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.
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
24 #ifndef AVUTIL_RANDOM_H
25 #define AVUTIL_RANDOM_H
27 #define AV_RANDOM_N 624
30 unsigned int mt
[AV_RANDOM_N
]; ///< the array for the state vector
31 int index
; ///< Current untempered value we use as the base.
35 void av_init_random(unsigned int seed
, AVRandomState
*state
); ///< 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.
36 void av_random_generate_untempered_numbers(AVRandomState
*state
); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop).
39 * Generates a random number from the interval [0,0xffffffff].
41 * Please do NOT use the Mersenne Twister, it is slow. Use the random generator
42 * from lfg.c/h or a simple LCG like state= state*1664525+1013904223.
43 * If you still choose to use MT, expect that you will have to provide
44 * some evidence that it makes a difference for the case where you use it.
46 static inline unsigned int av_random(AVRandomState
*state
)
50 // Regenerate the untempered numbers if we should...
51 if (state
->index
>= AV_RANDOM_N
)
52 av_random_generate_untempered_numbers(state
);
55 y
= state
->mt
[state
->index
++];
57 /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937 are.. */
59 y
^= (y
<< 7) & 0x9d2c5680;
60 y
^= (y
<< 15) & 0xefc60000;
66 /** Return random in range [0-1] as double. */
67 static inline double av_random_real1(AVRandomState
*state
)
69 /* divided by 2^32-1 */
70 return av_random(state
) * (1.0 / 4294967296.0);
73 #endif /* AVUTIL_RANDOM_H */