ref: b566c02d19b2e6321bb7e2090188feb0ed1e0c0a
dir: /sys/src/libc/port/frand.c/
#include	<u.h>
#include	<libc.h>
#define	MASK	0x7fffffffL
#define	NORM	(1.0/(1.0+MASK))
double
frand(void)
{
	double x;
	do {
		x = lrand() * NORM;
		x = (x + lrand()) * NORM;
	} while(x >= 1);
	return x;
}