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av_random() by Ryan Martell rdm4 name-server-seperator martellventures d0t com
Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer
parent
a264a081b2
commit
fbabf1e0b6
@ -17,9 +17,11 @@ OBJS= mathematics.o \
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fifo.o \
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tree.o \
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lzo.o \
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random.o \
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HEADERS = avutil.h common.h mathematics.h integer.h rational.h \
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intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h
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intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h \
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random.h
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NAME=avutil
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ifeq ($(BUILD_SHARED),yes)
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104
libavutil/random.c
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104
libavutil/random.c
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@ -0,0 +1,104 @@
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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 C-program 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 02110-1301 USA
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*/
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/**
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see http://en.wikipedia.org/wiki/Mersenne_twister for an explanation of this algorithm.
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*/
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#include <stdio.h>
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#include "random.h"
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//#define DEBUG
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#ifdef DEBUG
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#include "common.h"
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#include "log.h"
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#endif
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/* Period parameters */
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#define M 397
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#define A 0x9908b0df /* constant vector a */
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#define UPPER_MASK 0x80000000 /* most significant w-r bits */
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#define LOWER_MASK 0x7fffffff /* least significant r bits */
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/** initializes mt[AV_RANDOM_N] with a seed */
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void av_init_random(unsigned int seed, AVRandomState *state)
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{
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int index;
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/*
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This differs from the wikipedia article. Source is from the Makoto
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Makoto Matsumoto and Takuji Nishimura code, with the following comment:
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*/
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/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
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/* In the previous versions, MSBs of the seed affect */
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/* only MSBs of the array mt[]. */
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state->mt[0] = seed & 0xffffffff;
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for (index = 1; index < AV_RANDOM_N; index++) {
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unsigned int prev= state->mt[index - 1];
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state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff;
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}
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state->index= index; // will cause it to generate untempered numbers the first iteration
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}
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/** generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't) */
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void av_random_generate_untempered_numbers(AVRandomState *state)
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{
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int kk;
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unsigned int y;
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for (kk = 0; kk < AV_RANDOM_N - M; kk++) {
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y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
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state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A);
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}
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for (; kk < AV_RANDOM_N - 1; kk++) {
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y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
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state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A);
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}
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y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK);
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state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A);
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state->index = 0;
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}
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#ifdef DEBUG
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void av_benchmark_random(void)
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{
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int x=0;
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int i, j;
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AVRandomState state;
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av_init_random(0xdeadbeef, &state);
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for (j = 0; j < 100; j++) {
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START_TIMER;
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x+= av_random(&state);
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STOP_TIMER("first call to av_random");
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for (i = 1; i < AV_RANDOM_N; i++) {
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START_TIMER;
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x+= av_random(&state);
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STOP_TIMER("AV_RANDOM_N calls of av_random");
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}
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}
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av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
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}
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#endif
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69
libavutil/random.h
Normal file
69
libavutil/random.h
Normal file
@ -0,0 +1,69 @@
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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 C-program 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 02110-1301 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 [0-1] as double */
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static inline double av_random_real1(AVRandomState *state)
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{
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/* divided by 2^32-1 */
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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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