From fbabf1e0b600ac5e2a4ad85ac1c5dc38b0dfc7ef Mon Sep 17 00:00:00 2001 From: Michael Niedermayer Date: Thu, 8 Feb 2007 22:09:05 +0000 Subject: av_random() by Ryan Martell rdm4 name-server-seperator martellventures d0t com Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavutil/Makefile | 4 ++- libavutil/random.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++++ libavutil/random.h | 69 +++++++++++++++++++++++++++++++++++ 3 files changed, 176 insertions(+), 1 deletion(-) create mode 100644 libavutil/random.c create mode 100644 libavutil/random.h diff --git a/libavutil/Makefile b/libavutil/Makefile index 1e626fa..0640630 100644 --- a/libavutil/Makefile +++ b/libavutil/Makefile @@ -17,9 +17,11 @@ OBJS= mathematics.o \ fifo.o \ tree.o \ lzo.o \ + random.o \ HEADERS = avutil.h common.h mathematics.h integer.h rational.h \ - intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h + intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h \ + random.h NAME=avutil ifeq ($(BUILD_SHARED),yes) diff --git a/libavutil/random.c b/libavutil/random.c new file mode 100644 index 0000000..c3e71e6 --- /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 +#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 diff --git a/libavutil/random.h b/libavutil/random.h new file mode 100644 index 0000000..d9d08a5 --- /dev/null +++ b/libavutil/random.h @@ -0,0 +1,69 @@ +/* + * 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 + */ + +#ifndef AV_RANDOM_H +#define AV_RANDOM_H + +#define AV_RANDOM_N 624 + +typedef struct { + unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector + int index; ///< current untempered value we use as the base. +} AVRandomState; + + +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 +void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop) + +/** generates a random number on [0,0xffffffff]-interval */ +static inline unsigned int av_random(AVRandomState *state) +{ + unsigned int y; + + // regenerate the untempered numbers if we should... + if (state->index >= AV_RANDOM_N) + av_random_generate_untempered_numbers(state); + + // grab one... + y = state->mt[state->index++]; + + /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */ + y ^= (y >> 11); + y ^= (y << 7) & 0x9d2c5680; + y ^= (y << 15) & 0xefc60000; + y ^= (y >> 18); + + return y; +} + +/** return random in range [0-1] as double */ +static inline double av_random_real1(AVRandomState *state) +{ + /* divided by 2^32-1 */ + return av_random(state) * (1.0 / 4294967296.0); +} + +// only available if DEBUG is defined in the .c file +void av_benchmark_random(void); +#endif // AV_RANDOM_H + -- cgit v1.1