diff options
author | Michael Niedermayer <michaelni@gmx.at> | 2007-02-09 01:09:05 +0300 |
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committer | Michael Niedermayer <michaelni@gmx.at> | 2007-02-09 01:09:05 +0300 |
commit | fbabf1e0b600ac5e2a4ad85ac1c5dc38b0dfc7ef (patch) | |
tree | 2508bea8b0d0679a0e5110895ca18978122b2c55 /libavutil/random.c | |
parent | a264a081b20746a29231a013e7e9465d08aac0f1 (diff) |
av_random() by Ryan Martell rdm4 name-server-seperator martellventures d0t com
Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk
Diffstat (limited to 'libavutil/random.c')
-rw-r--r-- | libavutil/random.c | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/libavutil/random.c b/libavutil/random.c new file mode 100644 index 0000000000..c3e71e699c --- /dev/null +++ b/libavutil/random.c @@ -0,0 +1,104 @@ +/* + * Mersenne Twister Random Algorithm + * Copyright (c) 2006 Ryan Martell. + * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by + * Takuji Nishimura and Makoto Matsumoto. + * + * This file is part of FFmpeg. + * + * FFmpeg is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * FFmpeg is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with FFmpeg; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + + +/** +see http://en.wikipedia.org/wiki/Mersenne_twister for an explanation of this algorithm. +*/ +#include <stdio.h> +#include "random.h" + +//#define DEBUG + +#ifdef DEBUG +#include "common.h" +#include "log.h" +#endif + + +/* Period parameters */ +#define M 397 +#define A 0x9908b0df /* constant vector a */ +#define UPPER_MASK 0x80000000 /* most significant w-r bits */ +#define LOWER_MASK 0x7fffffff /* least significant r bits */ + +/** initializes mt[AV_RANDOM_N] with a seed */ +void av_init_random(unsigned int seed, AVRandomState *state) +{ + int index; + + /* + This differs from the wikipedia article. Source is from the Makoto + Makoto Matsumoto and Takuji Nishimura code, with the following comment: + */ + /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */ + /* In the previous versions, MSBs of the seed affect */ + /* only MSBs of the array mt[]. */ + state->mt[0] = seed & 0xffffffff; + for (index = 1; index < AV_RANDOM_N; index++) { + unsigned int prev= state->mt[index - 1]; + state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff; + } + state->index= index; // will cause it to generate untempered numbers the first iteration +} + +/** generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't) */ +void av_random_generate_untempered_numbers(AVRandomState *state) +{ + int kk; + unsigned int y; + + for (kk = 0; kk < AV_RANDOM_N - M; kk++) { + y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK); + state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A); + } + for (; kk < AV_RANDOM_N - 1; kk++) { + y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK); + state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A); + } + y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK); + state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A); + state->index = 0; +} + +#ifdef DEBUG +void av_benchmark_random(void) +{ + int x=0; + int i, j; + AVRandomState state; + + av_init_random(0xdeadbeef, &state); + for (j = 0; j < 100; j++) { + START_TIMER; + x+= av_random(&state); + STOP_TIMER("first call to av_random"); + for (i = 1; i < AV_RANDOM_N; i++) { + START_TIMER; + x+= av_random(&state); + STOP_TIMER("AV_RANDOM_N calls of av_random"); + } + } + av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); +} +#endif |