Add a multiplicative LFG for those thinking the additive is not good
[libav.git] / libavutil / lfg.h
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1/*
2 * Lagged Fibonacci PRNG
3 * Copyright (c) 2008 Michael Niedermayer
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#ifndef FFMPEG_LFG_H
23#define FFMPEG_LFG_H
24
25typedef struct {
26 unsigned int state[64];
27 int index;
28} AVLFG;
29
30void av_lfg_init(AVLFG *c, unsigned int seed);
31
2cf3c863 32/**
310d4424 33 * Gets the next random unsigned 32bit number using a ALFG.
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34 *
35 * Please also consider a simple LCG like state= state*1664525+1013904223,
36 * it may be good enough and faster for your specific use case.
37 */
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38static inline unsigned int av_lfg_get(AVLFG *c){
39 c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
40 return c->state[c->index++ & 63];
41}
42
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43/**
44 * Gets the next random unsigned 32bit number using a MLFG.
45 *
46 * Please also consider the av_lfg_get() above, it is faster.
47 */
48static inline unsigned int av_mlfg_get(AVLFG *c){
49 unsigned int a= c->state[(c->index-55) & 63];
50 unsigned int b= c->state[(c->index-24) & 63];
51 return c->state[c->index++ & 63] = a*b+a+b;
52}
53
2754fe8b 54#endif //FFMPEG_LFG_H