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Simple lagged fibonacci PRNG.

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3.5 times faster than our mersene twister.
10 times less memory needed. (=less cache trashing)

Originally committed as revision 14458 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2008-07-28 15:35:04 +00:00
parent 045e21cc19
commit 2754fe8ba5
2 changed files with 101 additions and 0 deletions
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64
libavutil/lfg.c Normal file
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/*
* 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 "lfg.h"
#include "md5.h"
#include "intreadwrite.h"
void av_cold 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;
}
#ifdef TEST
#include "log.h"
#include "common.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_random");
}
av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
return 0;
}
#endif

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/*
* 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
*/
#ifndef FFMPEG_LFG_H
#define FFMPEG_LFG_H
typedef struct {
unsigned int state[64];
int index;
} AVLFG;
void av_lfg_init(AVLFG *c, unsigned int seed);
static inline unsigned int av_lfg_get(AVLFG *c){
c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
return c->state[c->index++ & 63];
}
#endif //FFMPEG_LFG_H