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FFmpeg/libavutil/lfg.c
Ganesh Ajjanagadde 0c33ceda91 lavu/lfg-test: add simple sample mean, stddev checks
Also added a TODO to change to a proper normality test in the future.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanag@gmail.com>
2016-03-13 12:41:36 -04:00

119 lines
3.3 KiB
C

/*
* Lagged Fibonacci PRNG
* Copyright (c) 2008 Michael Niedermayer
*
* 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
*/
#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++) {
//av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
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;
double samp_mean = 0.0, samp_stddev = 0.0;
double samp0, samp1;
av_lfg_init(&state, 42);
for (i = 0; i < 1000; i += 2) {
double bmg_out[2];
av_bmg_get(&state, bmg_out);
samp0 = bmg_out[0] * stddev + mean;
samp1 = bmg_out[1] * stddev + mean;
samp_mean += samp0 + samp1;
samp_stddev += samp0 * samp0 + samp1 * samp1;
av_log(NULL, AV_LOG_INFO,
"%f\n%f\n",
samp0,
samp1);
}
/* TODO: add proper normality test */
samp_mean /= 1000;
samp_stddev /= 999;
samp_stddev -= (1000.0/999.0)*samp_mean*samp_mean;
samp_stddev = sqrt(samp_stddev);
av_log(NULL, AV_LOG_INFO, "sample mean : %f\n"
"true mean : %f\n"
"sample stddev: %f\n"
"true stddev : %f\n",
samp_mean, mean, samp_stddev, stddev);
}
return 0;
}
#endif