/* * 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