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2134
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1 /*
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2 * Lagged Fibonacci PRNG
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3 * Copyright (c) 2008 Michael Niedermayer
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4 *
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5 * This file is part of FFmpeg.
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6 *
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7 * FFmpeg is free software; you can redistribute it and/or
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8 * modify it under the terms of the GNU Lesser General Public
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9 * License as published by the Free Software Foundation; either
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10 * version 2.1 of the License, or (at your option) any later version.
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11 *
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12 * FFmpeg is distributed in the hope that it will be useful,
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13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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15 * Lesser General Public License for more details.
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16 *
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17 * You should have received a copy of the GNU Lesser General Public
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18 * License along with FFmpeg; if not, write to the Free Software
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19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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20 */
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21
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22 #ifndef AVUTIL_LFG_H
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23 #define AVUTIL_LFG_H
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24
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25 typedef struct AVLFG {
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26 unsigned int state[64];
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27 int index;
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28 } AVLFG;
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29
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30 void av_lfg_init(AVLFG *c, unsigned int seed);
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31
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32 /**
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33 * Get the next random unsigned 32-bit number using an ALFG.
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34 *
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35 * Please also consider a simple LCG like state= state*1664525+1013904223,
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36 * it may be good enough and faster for your specific use case.
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37 */
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38 static inline unsigned int av_lfg_get(AVLFG *c){
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39 c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
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40 return c->state[c->index++ & 63];
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41 }
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42
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43 /**
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44 * Get the next random unsigned 32-bit number using a MLFG.
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45 *
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46 * Please also consider av_lfg_get() above, it is faster.
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47 */
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48 static inline unsigned int av_mlfg_get(AVLFG *c){
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49 unsigned int a= c->state[(c->index-55) & 63];
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50 unsigned int b= c->state[(c->index-24) & 63];
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51 return c->state[c->index++ & 63] = 2*a*b+a+b;
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52 }
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53
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54 /**
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55 * Get the next two numbers generated by a Box-Muller Gaussian
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56 * generator using the random numbers issued by lfg.
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57 *
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58 * @param out array where the two generated numbers are placed
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59 */
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60 void av_bmg_get(AVLFG *lfg, double out[2]);
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61
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62 #endif /* AVUTIL_LFG_H */
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