Subversion Repositories planix.SVN

#include	<u.h>

#include	<libc.h>

/*

 *	algorithm by

 *	D. P. Mitchell & J. A. Reeds

 */

#define	LEN	607

#define	TAP	273

#define	MASK	0x7fffffffL

#define	A	48271

#define	M	2147483647

#define	Q	44488

#define	R	3399

#define	NORM	(1.0/(1.0+MASK))

static	ulong	rng_vec[LEN];

static	ulong*	rng_tap = rng_vec;

static	ulong*	rng_feed = 0;

static	Lock	lk;

static void

isrand(long seed)

{

	long lo, hi, x;

	int i;

	rng_tap = rng_vec;

	rng_feed = rng_vec+LEN-TAP;

	seed = seed%M;

	if(seed < 0)

		seed += M;

	if(seed == 0)

		seed = 89482311;

	x = seed;

	/*

	 *	Initialize by x[n+1] = 48271 * x[n] mod (2**31 - 1)

	 */

	for(i = -20; i < LEN; i++) {

		hi = x / Q;

		lo = x % Q;

		x = A*lo - R*hi;

		if(x < 0)

			x += M;

		if(i >= 0)

			rng_vec[i] = x;

	}

}

void

srand(long seed)

{

	lock(&lk);

	isrand(seed);

	unlock(&lk);

}

long

lrand(void)

{

	ulong x;

	lock(&lk);

	rng_tap--;

	if(rng_tap < rng_vec) {

		if(rng_feed == 0) {

			isrand(1);

			rng_tap--;

		}

		rng_tap += LEN;

	}

	rng_feed--;

	if(rng_feed < rng_vec)

		rng_feed += LEN;

	x = (*rng_feed + *rng_tap) & MASK;

	*rng_feed = x;

	unlock(&lk);

	return x;

}