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/*
* Lagged Fibonacci PRNG
* Copyright (c) 2008 Michael Niedermayer
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <inttypes.h>
#include <limits.h>
#include <math.h>
#include "lfg.h"
#include "md5.h"
#include "intreadwrite.h"
#include "attributes.h"
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
{
uint8_t tmp[16] = { 0 };
int i;
for (i = 8; i < 64; i += 4) {
AV_WL32(tmp, seed);
tmp[4] = i;
av_md5_sum(tmp, tmp, 16);
c->state[i ] = AV_RL32(tmp);
c->state[i + 1] = AV_RL32(tmp + 4);
c->state[i + 2] = AV_RL32(tmp + 8);
c->state[i + 3] = AV_RL32(tmp + 12);
}
c->index = 0;
}
void av_bmg_get(AVLFG *lfg, double out[2])
{
double x1, x2, w;
do {
x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
w = x1 * x1 + x2 * x2;
} while (w >= 1.0);
w = sqrt((-2.0 * log(w)) / w);
out[0] = x1 * w;
out[1] = x2 * w;
}
#ifdef TEST
#include "log.h"
#include "timer.h"
int main(void)
{
int x = 0;
int i, j;
AVLFG state;
av_lfg_init(&state, 0xdeadbeef);
for (j = 0; j < 10000; j++) {
START_TIMER
for (i = 0; i < 624; i++)
x += av_lfg_get(&state);
STOP_TIMER("624 calls of av_lfg_get");
}
av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
/* BMG usage example */
{
double mean = 1000;
double stddev = 53;
av_lfg_init(&state, 42);
for (i = 0; i < 1000; i += 2) {
double bmg_out[2];
av_bmg_get(&state, bmg_out);
av_log(NULL, AV_LOG_INFO,
"%f\n%f\n",
bmg_out[0] * stddev + mean,
bmg_out[1] * stddev + mean);
}
}
return 0;
}
#endif
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