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 #include <stdint.h>
26 
27 /**
28  * Context structure for the Lagged Fibonacci PRNG.
29  * The exact layout, types and content of this struct may change and should
30  * not be accessed directly. Only its sizeof() is guranteed to stay the same
31  * to allow easy instanciation.
32  */
33 typedef struct AVLFG {
34  unsigned int state[64];
35  int index;
36 } AVLFG;
37 
38 void av_lfg_init(AVLFG *c, unsigned int seed);
39 
40 /**
41  * Seed the state of the ALFG using binary data.
42  *
43  * Return value: 0 on success, negative value (AVERROR) on failure.
44  */
45 int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length);
46 
47 /**
48  * Get the next random unsigned 32-bit number using an ALFG.
49  *
50  * Please also consider a simple LCG like state= state*1664525+1013904223,
51  * it may be good enough and faster for your specific use case.
52  */
53 static inline unsigned int av_lfg_get(AVLFG *c){
54  unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
55  c->index += 1U;
56  return a;
57 }
58 
59 /**
60  * Get the next random unsigned 32-bit number using a MLFG.
61  *
62  * Please also consider av_lfg_get() above, it is faster.
63  */
64 static inline unsigned int av_mlfg_get(AVLFG *c){
65  unsigned int a= c->state[(c->index-55) & 63];
66  unsigned int b= c->state[(c->index-24) & 63];
67  a = c->state[c->index & 63] = 2*a*b+a+b;
68  c->index += 1U;
69  return a;
70 }
71 
72 /**
73  * Get the next two numbers generated by a Box-Muller Gaussian
74  * generator using the random numbers issued by lfg.
75  *
76  * @param out array where the two generated numbers are placed
77  */
78 void av_bmg_get(AVLFG *lfg, double out[2]);
79 
80 #endif /* AVUTIL_LFG_H */
Context structure for the Lagged Fibonacci PRNG.
Definition: lfg.h:33
void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:32
int index
Definition: lfg.h:35
ptrdiff_t const GLvoid * data
Definition: opengl_enc.c:100
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:36
uint8_t
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
static unsigned int av_mlfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using a MLFG.
Definition: lfg.h:64
#define U(x)
Definition: vp56_arith.h:37
GLsizei GLsizei * length
Definition: opengl_enc.c:114
#define b
Definition: input.c:41
int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length)
Seed the state of the ALFG using binary data.
Definition: lfg.c:64
static unsigned int seed
Definition: videogen.c:78
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:53
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...
Definition: lfg.c:49
unsigned int state[64]
Definition: lfg.h:34
FILE * out
Definition: movenc.c:54