shithub: plan9front

ref: f5c6a870bfb6d92f623aaa42bb60f074638e37fe
dir: /sys/src/libsec/port/nfastrand.c/

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#include "os.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)
		sysfatal("nfastrand: n too large");

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