mirror of
https://git.code.sf.net/p/quake/quakeforge
synced 2024-11-14 08:50:58 +00:00
91a686d1f5
mtwist_rand_0_1 produces numbers in the range [0, 1) and mtwist_rand_m1_1 produces numbers in the range (-1, 1). The numbers will not be denormal, so the distribution should be fairly uniform (as much as Mersenne Twister itself is), but this needs proper testing. 0 is included for the mtwist_rand_0_1 as it seems useful, but -1 is not included in mtwist_rand_m1_1 in order to keep the extremes of the distribution balanced around 0.
105 lines
2.9 KiB
C
105 lines
2.9 KiB
C
/*
|
|
mersenne.c
|
|
|
|
Mersenne Twister PRNG
|
|
|
|
Copyright (C) 2013 Bill Currie <bill@taniwha.org>
|
|
|
|
Author: Bill Currie <bill@taniwha.org>
|
|
Date: 2013/01/21
|
|
|
|
This program is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU General Public License
|
|
as published by the Free Software Foundation; either version 2
|
|
of the License, or (at your option) any later version.
|
|
|
|
This program 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 General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program; if not, write to:
|
|
|
|
Free Software Foundation, Inc.
|
|
59 Temple Place - Suite 330
|
|
Boston, MA 02111-1307, USA
|
|
|
|
*/
|
|
#ifdef HAVE_CONFIG_H
|
|
# include "config.h"
|
|
#endif
|
|
|
|
/* This implementation is based on the pseudo-code given on
|
|
http://en.wikipedia.org/wiki/Mersenne_twister (as of the above date) with
|
|
some references to the code available from
|
|
http://www.cs.hmc.edu/~geoff/mtwist.html
|
|
|
|
The main difference is the actual generator has been modified such that
|
|
rather than pre-generating the 624 untempered values and then
|
|
regenerating new ones every 624th call, one single untempered value is
|
|
generated every call. While the per-call time will be higher for this
|
|
implementation, it should be constant and should also be very close to
|
|
the averate call time of the standard implementation.
|
|
|
|
The code has been tested by generating 2048 values with both
|
|
implementations using the same seed (0xdeadbeef) and comparing the output.
|
|
There were no differences.
|
|
*/
|
|
|
|
#define IMPLEMENT_MTWIST_Funcs
|
|
#include "QF/mersenne.h"
|
|
|
|
#define KNUTH_MULT 1812433253ul // 0x6c078965
|
|
#define KNUTH_SHIFT 30
|
|
#define HIGH_BITS 0x80000000
|
|
#define LOW_BITS 0x7fffffff
|
|
#define MT_RECURRENCE 0x9908b0df
|
|
#define MT_TEMPER_U 11
|
|
#define MT_TEMPER_S 7
|
|
#define MT_TEMPER_T 15
|
|
#define MT_TEMPER_L 18
|
|
#define MT_TEMPER_B 0x9d2c5680
|
|
#define MT_TEMPER_C 0xefc60000
|
|
#define MT_FEEDBACK 397
|
|
|
|
#define MT state->state
|
|
|
|
void
|
|
mtwist_seed (mtstate_t *state, uint32_t seed)
|
|
{
|
|
int i;
|
|
|
|
state->index = 0;
|
|
MT[0] = seed;
|
|
for (i = 1; i < MT_STATE_SIZE; i++) {
|
|
MT[i] = KNUTH_MULT * (MT[i - 1] ^ (MT[i - 1] >> KNUTH_SHIFT)) + i;
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
mtwist_generate (mtstate_t *state, int i)
|
|
{
|
|
uint32_t y;
|
|
static const uint32_t recurrence[] = { 0, MT_RECURRENCE };
|
|
|
|
y = (MT[i] & HIGH_BITS) | (MT[(i + 1) % MT_STATE_SIZE] & LOW_BITS);
|
|
MT[i] = MT[(i + MT_FEEDBACK) % MT_STATE_SIZE] ^ (y >> 1);
|
|
MT[i] ^= recurrence[y & 1];
|
|
}
|
|
|
|
uint32_t
|
|
mtwist_rand (mtstate_t *state)
|
|
{
|
|
uint32_t y;
|
|
|
|
mtwist_generate (state, state->index);
|
|
y = MT[state->index];
|
|
y ^= (y >> MT_TEMPER_U);
|
|
y ^= (y << MT_TEMPER_S) & MT_TEMPER_B;
|
|
y ^= (y << MT_TEMPER_T) & MT_TEMPER_C;
|
|
y ^= (y >> MT_TEMPER_L);
|
|
state->index = (state->index + 1) % MT_STATE_SIZE;
|
|
return y;
|
|
}
|