PeerStreamer

/*

 * 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 AVUTIL_LFG_H

#define AVUTIL_LFG_H

typedef struct {

    unsigned int state[64];

    int index;

} AVLFG;

void av_lfg_init(AVLFG *c, unsigned int seed);

/**

 * Gets the next random unsigned 32-bit number using an ALFG.

 *

 * Please also consider a simple LCG like state= state*1664525+1013904223,

 * it may be good enough and faster for your specific use case.

 */

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];

}

/**

 * Gets the next random unsigned 32-bit number using a MLFG.

 *

 * Please also consider av_lfg_get() above, it is faster.

 */

static inline unsigned int av_mlfg_get(AVLFG *c){

    unsigned int a= c->state[(c->index-55) & 63];

    unsigned int b= c->state[(c->index-24) & 63];

    return c->state[c->index++ & 63] = 2*a*b+a+b;

}

#endif /* AVUTIL_LFG_H */