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Implement the Mersenne Twister PRNG.

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This gives QF a consistent qualilty PRNG on all platforms. The
implementation is slightly different from the standard, but gives the same
results for the same speed (details in mersenne.c).
This commit is contained in:
Bill Currie 2013-01-21 20:05:16 +09:00
parent 3de67589a3
commit 5188644e75
4 changed files with 153 additions and 3 deletions
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4
include/QF/Makefile.am
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@ -4,8 +4,8 @@ nobase_pkginclude_HEADERS = \
alloc.h bspfile.h cbuf.h cdaudio.h checksum.h clip_hull.h cmd.h \
console.h crc.h csqc.h cvar.h dstring.h draw.h gib.h hash.h hl.h \
idparse.h image.h in_event.h info.h input.h iqm.h joystick.h keys.h \
link.h llist.h locs.h mathlib.h mdfour.h model.h modelgen.h msg.h \
object.h pak.h pakfile.h pcx.h png.h plugin.h pr_comp.h pr_debug.h \
link.h llist.h locs.h mathlib.h mdfour.h mersenne.h model.h modelgen.h \
msg.h object.h pak.h pakfile.h pcx.h png.h plugin.h pr_comp.h pr_debug.h \
pr_obj.h progs.h qargs.h qdefs.h qendian.h qfplist.h qtypes.h quakefs.h \
quakeio.h render.h riff.h ruamoko.h set.h screen.h script.h sizebuf.h \
skin.h sound.h spritegn.h sys.h teamplay.h tga.h uint32.h va.h \

46
include/QF/mersenne.h Normal file
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@ -0,0 +1,46 @@
/*
mersenne.h
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
*/
#ifndef __QF_mersenne_h
#define __QF_mersenne_h
#include "QF/qtypes.h"
#define MT_STATE_SIZE 624
typedef struct {
uint32_t state[MT_STATE_SIZE];
int index;
} mtstate_t;
void mtwist_seed (mtstate_t *state, uint32_t seed);
uint32_t mtwist_rand (mtstate_t *state);
#endif//__QF_mersenne_h

2
libs/util/Makefile.am
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@ -51,7 +51,7 @@ libQFutil_la_DEPENDENCIES= $(asm)
libQFutil_la_SOURCES= \
bspfile.c buildnum.c cbuf.c checksum.c cmd.c crc.c cvar.c dstring.c \
fendian.c hash.c idparse.c info.c link.c llist.c \
mathlib.c mdfour.c msg.c pakfile.c plugin.c qargs.c qendian.c \
mathlib.c mdfour.c mersenne.c msg.c pakfile.c plugin.c qargs.c qendian.c \
qfplist.c quakefs.c quakeio.c riff.c script.c set.c sizebuf.c string.c \
sys.c va.c ver_check.c vrect.c wad.c wadfile.c zone.c \
$(dirent) $(fnmatch) $(getopt)

104
libs/util/mersenne.c Normal file
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@ -0,0 +1,104 @@
/*
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.
*/
#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;
}