mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2024-12-26 17:32:06 +00:00
105 lines
3.4 KiB
C
105 lines
3.4 KiB
C
/*
|
|
* 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
|