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libavutil/random.h

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00001 /*
00002  * Mersenne Twister PRNG algorithm
00003  * Copyright (c) 2006 Ryan Martell
00004  * Based on a C program for MT19937, with initialization improved 2002/1/26.
00005  * Coded by Takuji Nishimura and Makoto Matsumoto.
00006  *
00007  * This file is part of FFmpeg.
00008  *
00009  * FFmpeg is free software; you can redistribute it and/or
00010  * modify it under the terms of the GNU Lesser General Public
00011  * License as published by the Free Software Foundation; either
00012  * version 2.1 of the License, or (at your option) any later version.
00013  *
00014  * FFmpeg is distributed in the hope that it will be useful,
00015  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00016  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00017  * Lesser General Public License for more details.
00018  *
00019  * You should have received a copy of the GNU Lesser General Public
00020  * License along with FFmpeg; if not, write to the Free Software
00021  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00022  */
00023 
00024 #ifndef AVUTIL_RANDOM_H
00025 #define AVUTIL_RANDOM_H
00026 
00027 #define AV_RANDOM_N 624
00028 
00029 #include "avutil.h"
00030 #include "common.h"
00031 
00032 typedef struct {
00033     unsigned int mt[AV_RANDOM_N]; 
00034     int index; 
00035 } AVRandomState;
00036 
00037 
00038 #if LIBAVUTIL_VERSION_MAJOR < 50
00039 attribute_deprecated void av_init_random(unsigned int seed, AVRandomState *state);
00040 #endif
00041 void av_random_init(AVRandomState *state, unsigned int seed); 
00042 void av_random_generate_untempered_numbers(AVRandomState *state); 
00043 
00052 static inline unsigned int av_random(AVRandomState *state)
00053 {
00054     unsigned int y;
00055 
00056     // Regenerate the untempered numbers if we should...
00057     if (state->index >= AV_RANDOM_N)
00058         av_random_generate_untempered_numbers(state);
00059 
00060     // Grab one...
00061     y = state->mt[state->index++];
00062 
00063     /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937 are.. */
00064     y ^= (y >> 11);
00065     y ^= (y << 7) & 0x9d2c5680;
00066     y ^= (y << 15) & 0xefc60000;
00067     y ^= (y >> 18);
00068 
00069     return y;
00070 }
00071 
00073 static inline double av_random_real1(AVRandomState *state)
00074 {
00075     /* divided by 2^32-1 */
00076     return av_random(state) * (1.0 / 4294967296.0);
00077 }
00078 
00079 #endif /* AVUTIL_RANDOM_H */

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