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lfg.c
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1 /*
2  * This file is part of FFmpeg.
3  *
4  * FFmpeg is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU Lesser General Public
6  * License as published by the Free Software Foundation; either
7  * version 2.1 of the License, or (at your option) any later version.
8  *
9  * FFmpeg is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12  * Lesser General Public License for more details.
13  *
14  * You should have received a copy of the GNU Lesser General Public
15  * License along with FFmpeg; if not, write to the Free Software
16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17  */
18 
19 #include "libavutil/log.h"
20 #include "libavutil/timer.h"
21 #include "libavutil/lfg.h"
22 
23 int main(void)
24 {
25  int x = 0;
26  int i, j;
27  AVLFG state;
28 
29  av_lfg_init(&state, 0xdeadbeef);
30  for (j = 0; j < 10000; j++) {
32  for (i = 0; i < 624; i++) {
33  //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
34  x += av_lfg_get(&state);
35  }
36  STOP_TIMER("624 calls of av_lfg_get");
37  }
38  av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
39 
40  /* BMG usage example */
41  {
42  double mean = 1000;
43  double stddev = 53;
44  double samp_mean = 0.0, samp_stddev = 0.0;
45  double samp0, samp1;
46 
47  av_lfg_init(&state, 42);
48 
49  for (i = 0; i < 1000; i += 2) {
50  double bmg_out[2];
51  av_bmg_get(&state, bmg_out);
52  samp0 = bmg_out[0] * stddev + mean;
53  samp1 = bmg_out[1] * stddev + mean;
54  samp_mean += samp0 + samp1;
55  samp_stddev += samp0 * samp0 + samp1 * samp1;
57  "%f\n%f\n",
58  samp0,
59  samp1);
60  }
61  /* TODO: add proper normality test */
62  samp_mean /= 1000;
63  samp_stddev /= 999;
64  samp_stddev -= (1000.0/999.0)*samp_mean*samp_mean;
65  samp_stddev = sqrt(samp_stddev);
66  av_log(NULL, AV_LOG_INFO, "sample mean : %f\n"
67  "true mean : %f\n"
68  "sample stddev: %f\n"
69  "true stddev : %f\n",
70  samp_mean, mean, samp_stddev, stddev);
71  }
72 
73  return 0;
74 }
Definition: lfg.h:25
#define NULL
Definition: coverity.c:32
uint64_t i
Definition: intfloat.h:33
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:47
high precision timer, useful to profile code
#define av_log(a,...)
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:176
#define AV_LOG_INFO
Standard information.
Definition: log.h:187
#define START_TIMER
Definition: timer.h:94
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:38
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:30
static struct @228 state
#define STOP_TIMER(id)
Definition: timer.h:95
int main(void)
Definition: lfg.c:23