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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
*/
/**
see http://en.wikipedia.org/wiki/Mersenne_twister for an explanation of this algorithm.
*/
#include <stdio.h>
#include "random.h"
/* Period parameters */
#define M 397
#define A 0x9908b0df /* constant vector a */
#define UPPER_MASK 0x80000000 /* most significant w-r bits */
#define LOWER_MASK 0x7fffffff /* least significant r bits */
/** initializes mt[AV_RANDOM_N] with a seed */
void av_init_random(unsigned int seed, AVRandomState *state)
{
int index;
/*
This differs from the wikipedia article. Source is from the
Makoto Matsumoto and Takuji Nishimura code, with the following comment:
*/
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
state->mt[0] = seed & 0xffffffff;
for (index = 1; index < AV_RANDOM_N; index++) {
unsigned int prev= state->mt[index - 1];
state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff;
}
state->index= index; // will cause it to generate untempered numbers the first iteration
}
/** generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't) */
void av_random_generate_untempered_numbers(AVRandomState *state)
{
int kk;
unsigned int y;
for (kk = 0; kk < AV_RANDOM_N - M; kk++) {
y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A);
}
for (; kk < AV_RANDOM_N - 1; kk++) {
y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A);
}
y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK);
state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A);
state->index = 0;
}
#ifdef TEST
#include "common.h"
#include "log.h"
int main(void)
{
int x=0;
int i, j;
AVRandomState state;
av_init_random(0xdeadbeef, &state);
for (j = 0; j < 10000; j++) {
START_TIMER
for (i = 0; i < 624; i++) {
x+= av_random(&state);
}
STOP_TIMER("624 calls of av_random");
}
av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
return 0;
}
#endif
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