ffmpeg / libavutil / random.h @ 25e4f8aa
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/*


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* Mersenne Twister Random Algorithm

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* Copyright (c) 2006 Ryan Martell.

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* Based on A Cprogram 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 021101301 USA

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*/

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#ifndef AV_RANDOM_H

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#define AV_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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/** generates a random number on [0,0xffffffff]interval */

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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 [01] as double */

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static inline double av_random_real1(AVRandomState *state) 
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{ 
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/* divided by 2^321 */

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return av_random(state) * (1.0 / 4294967296.0); 
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} 
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// only available if DEBUG is defined in the .c file

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void av_benchmark_random(void); 
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#endif // AV_RANDOM_H 
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