Commit fbabf1e0 authored by Michael Niedermayer's avatar Michael Niedermayer
Browse files

av_random() by Ryan Martell rdm4 name-server-seperator martellventures d0t com

Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk
parent a264a081
......@@ -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)
......
/*
* 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
/*
* 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
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