Re: [Libvisual-devel] randomness work.

[Vitaly V. B. <vit...@us...>]

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