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lfg.h
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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 AVUTIL_LFG_H
#define AVUTIL_LFG_H
#include <stdint.h>
/**
* Context structure for the Lagged Fibonacci PRNG.
* The exact layout, types and content of this struct may change and should
* not be accessed directly. Only its `sizeof()` is guaranteed to stay the same
* to allow easy instantiation.
*/
typedef struct AVLFG {
unsigned int state[64];
int index;
} AVLFG;
void av_lfg_init(AVLFG *c, unsigned int seed);
/**
* Seed the state of the ALFG using binary data.
*
* @return 0 on success, negative value (AVERROR) on failure.
*/
int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);
/**
* Get 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){
unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
c->index += 1U;
return a;
}
/**
* Get 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];
a = c->state[c->index & 63] = 2*a*b+a+b;
c->index += 1U;
return a;
}
/**
* Get the next two numbers generated by a Box-Muller Gaussian
* generator using the random numbers issued by lfg.
*
* @param lfg pointer to the context structure
* @param out array where the two generated numbers are placed
*/
void av_bmg_get(AVLFG *lfg, double out[2]);
#endif /* AVUTIL_LFG_H */
av_lfg_init
void av_lfg_init(AVLFG *c, unsigned int seed)
av_lfg_get
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition lfg.h:53
av_bmg_get
void av_bmg_get(AVLFG *lfg, double out[2])
Get the next two numbers generated by a Box-Muller Gaussian generator using the random numbers issued...
av_mlfg_get
static unsigned int av_mlfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using a MLFG.
Definition lfg.h:64
av_lfg_init_from_data
int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length)
Seed the state of the ALFG using binary data.
AVLFG
Context structure for the Lagged Fibonacci PRNG.
Definition lfg.h:33
AVLFG::state
unsigned int state[64]
Definition lfg.h:34
AVLFG::index
int index
Definition lfg.h:35