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/*
* Mersenne Twister Random Algorithm
* Copyright (c) 2006 Ryan Martell.
* Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
* Takuji Nishimura and Makoto Matsumoto.
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef FFMPEG_RANDOM_H
#define FFMPEG_RANDOM_H
#define AV_RANDOM_N 624
typedef struct {
unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
int index; ///< current untempered value we use as the base.
} AVRandomState;
void av_init_random(unsigned int seed, AVRandomState *state); ///< to be inlined, the struct must be visible, so it doesn't make sense to try and keep it opaque with malloc/free like calls
void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
/**
* generates a random number on [0,0xffffffff]-interval
*
* Please do NOT use the mersenne twister, it is slow, use the random generator
* from lfg.c/h or a simple LCG like state= state*1664525+1013904223.
* If you still choose to use MT, expect that you will have to provide
* some evidence that it makes a difference for the case where you use it.
*/
static inline unsigned int av_random(AVRandomState *state)
{
unsigned int y;
// regenerate the untempered numbers if we should...
if (state->index >= AV_RANDOM_N)
av_random_generate_untempered_numbers(state);
// grab one...
y = state->mt[state->index++];
/* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
y ^= (y >> 11);
y ^= (y << 7) & 0x9d2c5680;
y ^= (y << 15) & 0xefc60000;
y ^= (y >> 18);
return y;
}
/** return random in range [0-1] as double */
static inline double av_random_real1(AVRandomState *state)
{
/* divided by 2^32-1 */
return av_random(state) * (1.0 / 4294967296.0);
}
#endif /* FFMPEG_RANDOM_H */
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