FFmpeg: libavutil/lfg.h Source File

FFmpeg
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 AVUTIL_LFG_H
23 #define AVUTIL_LFG_H
24 
25  typedef struct AVLFG {
26   unsigned int state[64];
27   int index;
28 } AVLFG;
29 
30 void av_lfg_init(AVLFG *c, unsigned int seed);
31 
32 /**
33  * Get the next random unsigned 32-bit number using an ALFG.
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  */
38  static 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 
43 /**
44  * Get the next random unsigned 32-bit number using a MLFG.
45  *
46  * Please also consider av_lfg_get() above, it is faster.
47  */
48  static 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] = 2*a*b+a+b;
52 }
53 
54 /**
55  * Get the next two numbers generated by a Box-Muller Gaussian
56  * generator using the random numbers issued by lfg.
57  *
58  * @param out array where the two generated numbers are placed
59  */
60 void av_bmg_get(AVLFG *lfg, double out[2]);
61 
62 #endif /* AVUTIL_LFG_H */
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