[unix-history] / usr / src / sys / libkern / random.c

/*-
 * Copyright (c) 1992 The Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 *
 *	@(#)random.c	7.1 (Berkeley) %G%
 */

#include "libkern.h"

/*
 * Pseudo-random number generator for randomizing the profiling clock,
 * and whatever else we might use it for.  The result is uniform on
 * [0, 2^31 - 1].
 */
u_long
random()
{
	static u_long randseed = 1;
	register long x, hi, lo, t;

	/*
	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
	 * From "Random number generators: good ones are hard to find",
	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
	 * October 1988, p. 1195.
	 */
	x = randseed;
	hi = x / 127773;
	lo = x % 127773;
	t = 16807 * lo - 2836 * hi;
	if (t <= 0)
		t += 0x7fffffff;
	randseed = t;
	return (t);
}
Commit	Line	Data
a4681977 CT	1	/*-
	2	* Copyright (c) 1992 The Regents of the University of California.
	3	* All rights reserved.
	4	*
	5	* %sccs.include.redist.c%
	6	*
	7	* @(#)random.c 7.1 (Berkeley) %G%
	8	*/
	9
	10	#include "libkern.h"
	11
	12	/*
	13	* Pseudo-random number generator for randomizing the profiling clock,
	14	* and whatever else we might use it for. The result is uniform on
	15	* [0, 2^31 - 1].
	16	*/
	17	u_long
	18	random()
	19	{
	20	static u_long randseed = 1;
	21	register long x, hi, lo, t;
	22
	23	/*
	24	* Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
	25	* From "Random number generators: good ones are hard to find",
	26	* Park and Miller, Communications of the ACM, vol. 31, no. 10,
	27	* October 1988, p. 1195.
	28	*/
	29	x = randseed;
	30	hi = x / 127773;
	31	lo = x % 127773;
	32	t = 16807 * lo - 2836 * hi;
	33	if (t <= 0)
	34	t += 0x7fffffff;
	35	randseed = t;
	36	return (t);
	37	}