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74 lines
2.6 KiB
C
74 lines
2.6 KiB
C
/*
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* Mersenne Twister Random Algorithm
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* Copyright (c) 2006 Ryan Martell.
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* Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
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* Takuji Nishimura and Makoto Matsumoto.
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef FFMPEG_RANDOM_H
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#define FFMPEG_RANDOM_H
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#define AV_RANDOM_N 624
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typedef struct {
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unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
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int index; ///< current untempered value we use as the base.
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} AVRandomState;
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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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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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/**
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* generates a random number on [0,0xffffffff]-interval
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*
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* Please do NOT use the mersenne twister, it is slow, use the random generator
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* from lfg.c/h or a simple LCG like state= state*1664525+1013904223.
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* If you still choose to use MT, expect that you will have to provide
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* some evidence that it makes a difference for the case where you use it.
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*/
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static inline unsigned int av_random(AVRandomState *state)
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{
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unsigned int y;
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// regenerate the untempered numbers if we should...
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if (state->index >= AV_RANDOM_N)
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av_random_generate_untempered_numbers(state);
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// grab one...
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y = state->mt[state->index++];
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/* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
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y ^= (y >> 11);
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y ^= (y << 7) & 0x9d2c5680;
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y ^= (y << 15) & 0xefc60000;
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y ^= (y >> 18);
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return y;
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}
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/** return random in range [0-1] as double */
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static inline double av_random_real1(AVRandomState *state)
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{
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/* divided by 2^32-1 */
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return av_random(state) * (1.0 / 4294967296.0);
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}
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#endif /* FFMPEG_RANDOM_H */
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