ffmpeg / libavutil / random.h @ 5b21bdab
History  View  Annotate  Download (2.37 KB)
1 
/*


2 
* Mersenne Twister Random Algorithm

3 
* Copyright (c) 2006 Ryan Martell.

4 
* Based on A Cprogram for MT19937, with initialization improved 2002/1/26. Coded by

5 
* Takuji Nishimura and Makoto Matsumoto.

6 
*

7 
* This file is part of FFmpeg.

8 
*

9 
* FFmpeg is free software; you can redistribute it and/or

10 
* modify it under the terms of the GNU Lesser General Public

11 
* License as published by the Free Software Foundation; either

12 
* version 2.1 of the License, or (at your option) any later version.

13 
*

14 
* FFmpeg is distributed in the hope that it will be useful,

15 
* but WITHOUT ANY WARRANTY; without even the implied warranty of

16 
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

17 
* Lesser General Public License for more details.

18 
*

19 
* You should have received a copy of the GNU Lesser General Public

20 
* License along with FFmpeg; if not, write to the Free Software

21 
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 021101301 USA

22 
*/

23  
24 
#ifndef FFMPEG_RANDOM_H

25 
#define FFMPEG_RANDOM_H

26  
27 
#define AV_RANDOM_N 624 
28  
29 
typedef struct { 
30 
unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector 
31 
int index; ///< current untempered value we use as the base. 
32 
} AVRandomState; 
33  
34  
35 
void av_init_random(unsigned int seed, AVRandomState *state); ///< to be inlined, the struct must be visible, so it doesn't make sense to try and keep it opaque with malloc/free like calls 
36 
void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop) 
37  
38 
/** generates a random number on [0,0xffffffff]interval */

39 
static inline unsigned int av_random(AVRandomState *state) 
40 
{ 
41 
unsigned int y; 
42  
43 
// regenerate the untempered numbers if we should...

44 
if (state>index >= AV_RANDOM_N)

45 
av_random_generate_untempered_numbers(state); 
46  
47 
// grab one...

48 
y = state>mt[state>index++]; 
49  
50 
/* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */

51 
y ^= (y >> 11);

52 
y ^= (y << 7) & 0x9d2c5680; 
53 
y ^= (y << 15) & 0xefc60000; 
54 
y ^= (y >> 18);

55  
56 
return y;

57 
} 
58  
59 
/** return random in range [01] as double */

60 
static inline double av_random_real1(AVRandomState *state) 
61 
{ 
62 
/* divided by 2^321 */

63 
return av_random(state) * (1.0 / 4294967296.0); 
64 
} 
65  
66 
// only available if DEBUG is defined in the .c file

67 
void av_benchmark_random(void); 
68  
69 
#endif /* FFMPEG_RANDOM_H */ 