lfg.h 1.93 KB
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/*
 * Lagged Fibonacci PRNG
 * Copyright (c) 2008 Michael Niedermayer
 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * 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.
 *
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 * Libav is distributed in the hope that it will be useful,
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 * 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
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

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#ifndef AVUTIL_LFG_H
#define AVUTIL_LFG_H
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typedef struct {
    unsigned int state[64];
    int index;
} AVLFG;

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

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/**
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 * Get the next random unsigned 32-bit number using an ALFG.
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 *
 * Please also consider a simple LCG like state= state*1664525+1013904223,
 * it may be good enough and faster for your specific use case.
 */
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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];
}

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/**
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 * Get the next random unsigned 32-bit number using a MLFG.
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 *
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 * Please also consider av_lfg_get() above, it is faster.
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 */
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];
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    return c->state[c->index++ & 63] = 2*a*b+a+b;
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}

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/**
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 * Get the next two numbers generated by a Box-Muller Gaussian
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 * generator using the random numbers issued by lfg.
 *
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 * @param out[2] array where the two generated numbers are placed
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 */
void av_bmg_get(AVLFG *lfg, double out[2]);

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#endif /* AVUTIL_LFG_H */