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| 1 /* | |
| 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. Cod
ed 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 02110-1301 USA | |
| 22 */ | |
| 23 | |
| 24 #ifndef AVUTIL_RANDOM_H | |
| 25 #define AVUTIL_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 does not make sense to try and keep it opaqu
e with malloc/free-like calls. | |
| 36 void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerat
e the untempered numbers (must be done every 624 iterations, or it will loop). | |
| 37 | |
| 38 /** | |
| 39 * Generates a random number from the interval [0,0xffffffff]. | |
| 40 * | |
| 41 * Please do NOT use the Mersenne Twister, it is slow. Use the random generator | |
| 42 * from lfg.c/h or a simple LCG like state= state*1664525+1013904223. | |
| 43 * If you still choose to use MT, expect that you will have to provide | |
| 44 * some evidence that it makes a difference for the case where you use it. | |
| 45 */ | |
| 46 static inline unsigned int av_random(AVRandomState *state) | |
| 47 { | |
| 48 unsigned int y; | |
| 49 | |
| 50 // Regenerate the untempered numbers if we should... | |
| 51 if (state->index >= AV_RANDOM_N) | |
| 52 av_random_generate_untempered_numbers(state); | |
| 53 | |
| 54 // Grab one... | |
| 55 y = state->mt[state->index++]; | |
| 56 | |
| 57 /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937
are.. */ | |
| 58 y ^= (y >> 11); | |
| 59 y ^= (y << 7) & 0x9d2c5680; | |
| 60 y ^= (y << 15) & 0xefc60000; | |
| 61 y ^= (y >> 18); | |
| 62 | |
| 63 return y; | |
| 64 } | |
| 65 | |
| 66 /** Return random in range [0-1] as double. */ | |
| 67 static inline double av_random_real1(AVRandomState *state) | |
| 68 { | |
| 69 /* divided by 2^32-1 */ | |
| 70 return av_random(state) * (1.0 / 4294967296.0); | |
| 71 } | |
| 72 | |
| 73 #endif /* AVUTIL_RANDOM_H */ | |
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Chromium Code Reviews
Issue 56129:
Update public FFmpeg header files from r16647 to r18286. (Closed)
