FFmpeg  3.2.18
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  unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
40  c->index += 1U;
41  return a;
42 }
43 
44 /**
45  * Get the next random unsigned 32-bit number using a MLFG.
46  *
47  * Please also consider av_lfg_get() above, it is faster.
48  */
49 static inline unsigned int av_mlfg_get(AVLFG *c){
50  unsigned int a= c->state[(c->index-55) & 63];
51  unsigned int b= c->state[(c->index-24) & 63];
52  a = c->state[c->index & 63] = 2*a*b+a+b;
53  c->index += 1U;
54  return a;
55 }
56 
57 /**
58  * Get the next two numbers generated by a Box-Muller Gaussian
59  * generator using the random numbers issued by lfg.
60  *
61  * @param out array where the two generated numbers are placed
62  */
63 void av_bmg_get(AVLFG *lfg, double out[2]);
64 
65 #endif /* AVUTIL_LFG_H */
Definition: lfg.h:25
void av_lfg_init(AVLFG *c, unsigned int seed)
int index
Definition: lfg.h:27
static unsigned int av_mlfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using a MLFG.
Definition: lfg.h:49
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:38
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...
unsigned int state[64]
Definition: lfg.h:26