1 | /*
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2 | * Mersenne Twister Random Algorithm
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3 | * Copyright (c) 2006 Ryan Martell.
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4 | * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
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5 | * Takuji Nishimura and Makoto Matsumoto.
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6 | *
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7 | * This file is part of FFmpeg.
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8 | *
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9 | * FFmpeg is free software; you can redistribute it and/or
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10 | * modify it under the terms of the GNU Lesser General Public
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11 | * License as published by the Free Software Foundation; either
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12 | * version 2.1 of the License, or (at your option) any later version.
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13 | *
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14 | * FFmpeg is distributed in the hope that it will be useful,
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15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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17 | * Lesser General Public License for more details.
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18 | *
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19 | * You should have received a copy of the GNU Lesser General Public
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20 | * License along with FFmpeg; if not, write to the Free Software
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21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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22 | */
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23 |
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24 | #ifndef AV_RANDOM_H
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25 | #define AV_RANDOM_H
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26 |
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27 | #define AV_RANDOM_N 624
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28 |
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29 | typedef struct {
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30 | unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
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31 | int index; ///< current untempered value we use as the base.
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32 | } AVRandomState;
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33 |
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34 |
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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
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36 | void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
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37 |
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38 | /** generates a random number on [0,0xffffffff]-interval */
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39 | static inline unsigned int av_random(AVRandomState *state)
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40 | {
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41 | unsigned int y;
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42 |
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43 | // regenerate the untempered numbers if we should...
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44 | if (state->index >= AV_RANDOM_N)
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45 | av_random_generate_untempered_numbers(state);
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46 |
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47 | // grab one...
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48 | y = state->mt[state->index++];
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49 |
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50 | /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
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51 | y ^= (y >> 11);
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52 | y ^= (y << 7) & 0x9d2c5680;
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53 | y ^= (y << 15) & 0xefc60000;
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54 | y ^= (y >> 18);
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55 |
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56 | return y;
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57 | }
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58 |
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59 | /** return random in range [0-1] as double */
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60 | static inline double av_random_real1(AVRandomState *state)
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61 | {
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62 | /* divided by 2^32-1 */
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63 | return av_random(state) * (1.0 / 4294967296.0);
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64 | }
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65 |
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66 | // only available if DEBUG is defined in the .c file
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67 | void av_benchmark_random(void);
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68 | #endif // AV_RANDOM_H
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69 |
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