libavutil/lfg.c

Go to the documentation of this file.

/*
 * 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

---