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in search of a good random number generator
Posted: Wed May 05, 2004 8:44 am
by jack
i been searching the web for a good random number generator, i found one by Paul Dixon.
http://www.masmforum.com/viewtopic.php?t=2740
i dapted it to PellesC, but need some help since i am still a C neophyte.
how can i optionally set the static variable rng? (to seed the rnd generator)
Code: Select all
double random(void)
{ static long long int rng=0x1954678542154787;
int result;
long long int mask2=0x7fffffffffffffff;
_asm{
movq mm0,rng; //get the last number
movq mm1,mm0;
psllq mm0,1;
pxor mm1,mm0;
pand mm1,mask2;
movq mm0,mm1;
psrlq mm1,62;
pxor mm0,mm1;
movq rng,mm0;
emms; //re-enable FPU
}
return frexp((double) rng,&result); //result between 0 and 1
}
Posted: Wed May 05, 2004 10:10 am
by blueznl
why don't you use the build in commands, or are they not fast enough?
x = random(n)
Posted: Wed May 05, 2004 10:15 am
by jack
my quest is for a 64 bit random number generator, to be included in a lib.
Posted: Wed May 05, 2004 10:16 am
by LarsG
maybe he's trying to do his own, or just understanding how it works?!?
Anyways.. I seem to recall there was some talk about this on the forum some time ago.. Perhaps you can find something if you search?!
Posted: Wed May 05, 2004 10:58 am
by Road Runner
Jack,
the code you posted is a 63 bit generator, for the 64 bit version see:
http://masmforum.com/viewtopic.php?t=2740&start=21 where it says "new version:"
Posted: Wed May 05, 2004 11:24 am
by dell_jockey
you might also want to google the net for 'Mersenne'. I'm working on that one for PB. Progress is slow, though....
Posted: Wed May 05, 2004 11:51 am
by jack
i think i got it solved, BTW which is better, numbers between 0 and 1 or -1 and 1.?
here's another, by MichaelW and Paul Dixon.
Code: Select all
#include <time.h>
#include <math.h>
double random2(void)
{ time_t t;
static int first_time=0;
static long long int shiftreg;//=0x1954678542154787;
long long int mask=0x6fffffffffffffff;
int temp;
if (first_time==0)
{
first_time=1;
time(&t)
shiftreg=t;
}
_asm{
movq mm0,shiftreg //get the last number
movq mm1,mm0 //take a copy
psrlq mm1,1 //do 1st tap bit (LSBs)
pxor mm0,mm1
psrlq mm1,2 //do 2nd tap bit (LSBs)
pxor mm0,mm1
psrlq mm1,1
pxor mm0,mm1 //do 3rd tap bit (LSBs), low 60 bits now done
//now correct for the high 4 bits
movq mm1,mm0 //take a copy
psllq mm1,60 //correct 3rd tap MSBs
pxor mm0,mm1
psllq mm1,1 //correct 2nd tap MSBs
pxor mm0,mm1
psllq mm1,2
pxor mm0,mm1 //correct 1st tap MSBs, all done
pxor mm0,mask
movq shiftreg,mm0 //write back the result
emms //re-enable FPU
}
return frexp((double) shiftreg,&temp);
}
all i added is the 'frexp' to extract the mantissa.