ref: fdf8af5e94a2989d1b3c94aa5c9f43139d2f56c6
dir: /sys/src/ape/lib/v/nrand.c/
#include <stdlib.h>
#define	MASK	0x7FFFFFFFL
#define	FRACT	(1.0 / (MASK + 1.0))
extern long lrand(void);
double
frand(void)
{
	return lrand() * FRACT;
}
nrand(int n)
{
	long slop, v;
	slop = MASK % n;
	do
		v = lrand();
	while(v <= slop);
	return v % n;
}