ffmpeg / libavutil / lfg.c @ d112aa5a
History  View  Annotate  Download (2.5 KB)
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 021101301 USA

20 
*/

21  
22 
#include <inttypes.h> 
23 
#include <limits.h> 
24 
#include <math.h> 
25 
#include "lfg.h" 
26 
#include "md5.h" 
27 
#include "intreadwrite.h" 
28 
#include "attributes.h" 
29  
30 
void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ 
31 
uint8_t tmp[16]={0}; 
32 
int i;

33  
34 
for(i=8; i<64; i+=4){ 
35 
AV_WL32(tmp, seed); tmp[4]=i;

36 
av_md5_sum(tmp, tmp, 16);

37 
c>state[i ]= AV_RL32(tmp); 
38 
c>state[i+1]= AV_RL32(tmp+4); 
39 
c>state[i+2]= AV_RL32(tmp+8); 
40 
c>state[i+3]= AV_RL32(tmp+12); 
41 
} 
42 
c>index=0;

43 
} 
44  
45 
void av_bmg_get(AVLFG *lfg, double out[2]) 
46 
{ 
47 
double x1, x2, w;

48  
49 
do {

50 
x1 = 2.0/UINT_MAX*av_lfg_get(lfg)  1.0; 
51 
x2 = 2.0/UINT_MAX*av_lfg_get(lfg)  1.0; 
52 
w = x1*x1 + x2*x2; 
53 
} while (w >= 1.0); 
54  
55 
w = sqrt((2.0 * log(w)) / w); 
56 
out[0] = x1 * w;

57 
out[1] = x2 * w;

58 
} 
59  
60 
#ifdef TEST

61 
#include "log.h" 
62 
#include "timer.h" 
63  
64 
int main(void) 
65 
{ 
66 
int x=0; 
67 
int i, j;

68 
AVLFG state; 
69  
70 
av_lfg_init(&state, 0xdeadbeef);

71 
for (j = 0; j < 10000; j++) { 
72 
START_TIMER 
73 
for (i = 0; i < 624; i++) { 
74 
// av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));

75 
x+=av_lfg_get(&state); 
76 
} 
77 
STOP_TIMER("624 calls of av_lfg_get");

78 
} 
79 
av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); 
80  
81 
/* BMG usage example */

82 
{ 
83 
double mean = 1000; 
84 
double stddev = 53; 
85  
86 
av_lfg_init(&state, 42);

87  
88 
for (i = 0; i < 1000; i += 2) { 
89 
double bmg_out[2]; 
90 
av_bmg_get(&state, bmg_out); 
91 
av_log(NULL, AV_LOG_INFO,

92 
"%f\n%f\n",

93 
bmg_out[0] * stddev + mean,

94 
bmg_out[1] * stddev + mean);

95 
} 
96 
} 
97  
98 
return 0; 
99 
} 
100 
#endif
