Thread: [Libvisual-devel] randomness work.

SourceForge Headquarters 225 Broadway Suite 1600 San Diego, CA 92101 +1 (858) 422-6466

I've put some of the randomness request in CVS, not yet finished tho.

Cheers,
Dennis

On Sat, 02 Oct 2004 13:35:13 +0200
Dennis Smit <sy...@yo...> wrote:

> I've put some of the randomness request in CVS, not yet finished tho.
when you convert unsigned int to float you loose entropy...
I think it's ok to add double variant of functions...

and one more thing... regarding to visual_random_int_range()
we should not use modulo operation unless we want to get _short_
repeating sequence. This function will be used mostly (i think)
to select some config profile like

load_new(configs[visual_random_int_range(0, sizeof(config)/sizeof(*config)-1)]);

we must use division op. here. smth like
uint32_t visual_random_int_range (int min, int max)
{
        return (visual_random_int () / (RANDOM_MAX/(max - min + 1))) + min;
}

Yes, it's slow but works better.

To check it compile&run

===============
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define val_a 1664525L
#define val_c 1013904223L
#define RMAX  4294967295U

#define X (1<<3)

static unsigned int _lv_randseed = 5415454;

unsigned int rnd()
{
	unsigned int a;
	a = _lv_randseed = val_a * _lv_randseed + val_c;
	a = a%X;
//	a = a/(RMAX/X);
	return a;
}

int main()
{
	unsigned int i, t=256;

	for (i=0;i<t;i++){
		printf("%d ", rnd());
		if (i%X == 0)
			printf("\n");
	}

}
===============
;)

-- 
Vitaly
GPG Key ID: F95A23B9

On Sun, 2004-10-03 at 18:48 +0300, Vitaly V. Bursov wrote:
> > I've put some of the randomness request in CVS, not yet finished tho.
> when you convert unsigned int to float you loose entropy...
> I think it's ok to add double variant of functions...

Go ahead :)

> and one more thing... regarding to visual_random_int_range()
> we should not use modulo operation unless we want to get _short_
> repeating sequence. This function will be used mostly (i think)
> to select some config profile like

Thanks for the demo program and for pointing this out, it has
been fixed in CVS.

Cheers,
Dennis

On Sun, 03 Oct 2004 18:11:35 +0200
Dennis Smit <sy...@yo...> wrote:

> On Sun, 2004-10-03 at 18:48 +0300, Vitaly V. Bursov wrote:
> > > I've put some of the randomness request in CVS, not yet finished tho.
> > when you convert unsigned int to float you loose entropy...
> > I think it's ok to add double variant of functions...
> 
> Go ahead :)
OK :)

few bits of code....

==========================
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define val_a 1664525L
#define val_c 1013904223L
#define RMAX  4294967295U

static unsigned int _lv_randseed = 5415454;

double rnd()
{
#if 0
	union {
		unsigned int a[2];
		double d;
	} val;
	unsigned int t;

	/* EXECUTION TIME
	 * alu maths = 5 clocks
	 * fsub = 4 clocks
	 * TOTAL: 9 for double
	 * WARNING: numbers should be ieee754 compliant
	 */

	t = _lv_randseed = val_a * _lv_randseed + val_c;
	val.a[0]=(t<<20);
	val.a[1]=0x3ff00000U | (t>>12);

	return (*(double*)&val.d)-1.0;
#else
	unsigned int t;
	double x;

	/* EXECUTION TIME
	 * fild - load int to fpu = 4 clocks
	 * fdiv - normalize result = 16/20/24 clocks for signle/double/ext prec.
	 * TOTAL: 24 for double
	 */

	t = _lv_randseed = val_a * _lv_randseed + val_c;
	x = (double)t/RMAX;
	return x;
#endif
}

double x = 0.0;

int main()
{
	unsigned int i, t=1000000000;

	for (i=0;i<t;i++){
		x += rnd();
	}

}
==========================

the same idea can be used to generate floats.

should I make a patch?

-- 
Vitaly
GPG Key ID: F95A23B9

On Sun, 2004-10-03 at 19:55 +0300, Vitaly V. Bursov wrote:
> the same idea can be used to generate floats.
> 
> should I make a patch?

Yeah sure, go ahead :)

Cheers,
Dennis

Here we go!...

Dennis, do you have some app to test this random() stuff?

-- 
Vitaly
GPG Key ID: F95A23B9

2004-10-04  Dennis Smit  <ds...@ne...>

        * libvisual/lv_random.*: A bit of a overhaul by
        Vitaly V. Bursov, thanks Vitaly :) (owyeah
        also added double, float)

Thanks a lot Vitaly, looks really good, I love how you've
solved the things with the #defines :)

I changed a few things, take a look at CVS.

Cheers,
Dennis

On Mon, 2004-10-04 at 01:37 +0300, Vitaly V. Bursov wrote:
> Here we go!...
> 
> Dennis, do you have some app to test this random() stuff?
> 

Thread: [Libvisual-devel] randomness work.

Audio visualisation library

libvisual-devel