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82 lines
2.5 KiB
C
82 lines
2.5 KiB
C
/*
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* Lagged Fibonacci PRNG
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* Copyright (c) 2008 Michael Niedermayer
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; 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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*/
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#ifndef AVUTIL_LFG_H
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#define AVUTIL_LFG_H
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#include <stdint.h>
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/**
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* Context structure for the Lagged Fibonacci PRNG.
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* The exact layout, types and content of this struct may change and should
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* not be accessed directly. Only its `sizeof()` is guaranteed to stay the same
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* to allow easy instanciation.
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*/
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typedef struct AVLFG {
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unsigned int state[64];
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int index;
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} AVLFG;
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void av_lfg_init(AVLFG *c, unsigned int seed);
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/**
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* Seed the state of the ALFG using binary data.
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*
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* @return 0 on success, negative value (AVERROR) on failure.
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*/
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int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);
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/**
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* Get the next random unsigned 32-bit number using an ALFG.
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*
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* Please also consider a simple LCG like state= state*1664525+1013904223,
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* it may be good enough and faster for your specific use case.
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*/
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static inline unsigned int av_lfg_get(AVLFG *c){
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unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
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c->index += 1U;
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return a;
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}
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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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*/
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static inline unsigned int av_mlfg_get(AVLFG *c){
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unsigned int a= c->state[(c->index-55) & 63];
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unsigned int b= c->state[(c->index-24) & 63];
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a = c->state[c->index & 63] = 2*a*b+a+b;
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c->index += 1U;
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return a;
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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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*
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* @param lfg pointer to the contex structure
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* @param out array where the two generated numbers are placed
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*/
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void av_bmg_get(AVLFG *lfg, double out[2]);
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#endif /* AVUTIL_LFG_H */
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