git: 9front

ref: bc7d74f09b53c39ada4e73ce73c01c6c0928f9f4
dir: /sys/src/cmd/unix/drawterm/libsec/nfastrand.c/

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#include <u.h>
#include <libc.h>
#include <libsec.h>

#define Maxrand	((1UL<<31)-1)

ulong
nfastrand(ulong n)
{
	ulong m, r;
	
	/*
	 * set m to the maximum multiple of n <= 2^31-1
	 * so we want a random number < m.
	 */
	if(n > Maxrand)
		abort();

	m = Maxrand - Maxrand % n;
	while((r = fastrand()) >= m)
		;
	return r%n;
}