2 * Mersenne Twister Random Algorithm
3 * Copyright (c) 2006 Ryan Martell.
4 * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
5 * Takuji Nishimura and Makoto Matsumoto.
7 * This file is part of FFmpeg.
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.
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.
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 02110-1301 USA
26 see http://en.wikipedia.org/wiki/Mersenne_twister for an explanation of this algorithm.
32 /* Period parameters */
34 #define A 0x9908b0df /* constant vector a */
35 #define UPPER_MASK 0x80000000 /* most significant w-r bits */
36 #define LOWER_MASK 0x7fffffff /* least significant r bits */
38 /** initializes mt[AV_RANDOM_N] with a seed */
39 void av_init_random(unsigned int seed
, AVRandomState
*state
)
44 This differs from the wikipedia article. Source is from the
45 Makoto Matsumoto and Takuji Nishimura code, with the following comment:
47 /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
48 /* In the previous versions, MSBs of the seed affect */
49 /* only MSBs of the array mt[]. */
50 state
->mt
[0] = seed
& 0xffffffff;
51 for (index
= 1; index
< AV_RANDOM_N
; index
++) {
52 unsigned int prev
= state
->mt
[index
- 1];
53 state
->mt
[index
] = (1812433253UL * (prev
^ (prev
>>30)) + index
) & 0xffffffff;
55 state
->index
= index
; // will cause it to generate untempered numbers the first iteration
58 /** generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't) */
59 void av_random_generate_untempered_numbers(AVRandomState
*state
)
64 for (kk
= 0; kk
< AV_RANDOM_N
- M
; kk
++) {
65 y
= (state
->mt
[kk
] & UPPER_MASK
) | (state
->mt
[kk
+ 1] & LOWER_MASK
);
66 state
->mt
[kk
] = state
->mt
[kk
+ M
] ^ (y
>> 1) ^ ((y
&1)*A
);
68 for (; kk
< AV_RANDOM_N
- 1; kk
++) {
69 y
= (state
->mt
[kk
] & UPPER_MASK
) | (state
->mt
[kk
+ 1] & LOWER_MASK
);
70 state
->mt
[kk
] = state
->mt
[kk
+ (M
- AV_RANDOM_N
)] ^ (y
>> 1) ^ ((y
&1)*A
);
72 y
= (state
->mt
[AV_RANDOM_N
- 1] & UPPER_MASK
) | (state
->mt
[0] & LOWER_MASK
);
73 state
->mt
[AV_RANDOM_N
- 1] = state
->mt
[M
- 1] ^ (y
>> 1) ^ ((y
&1)*A
);
86 av_init_random(0xdeadbeef, &state
);
87 for (j
= 0; j
< 10000; j
++) {
89 for (i
= 0; i
< 624; i
++) {
90 x
+= av_random(&state
);
92 STOP_TIMER("624 calls of av_random");
94 av_log(NULL
, AV_LOG_ERROR
, "final value:%X\n", x
);