xref: /openbsd-src/sys/lib/libkern/random.c (revision b27348b2082c02cb5227e0e4933400ad6739ec5a)

/*	$OpenBSD: random.c,v 1.10 2017/09/08 05:36:53 deraadt Exp $	*/
/*	$NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $	*/

/*-
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)random.c	8.1 (Berkeley) 6/10/93
 */

#include <sys/param.h>

#include <lib/libkern/libkern.h>

/*
 * Pseudo-random number generator for randomizing the profiling clock.
 * The result is uniform on [0, 2^31 - 1].
 */

u_int32_t
random(void)
{
	struct cpu_info *ci = curcpu();
	int32_t 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 = ci->ci_randseed;
	hi = x / 127773;
	lo = x % 127773;
	t = 16807 * lo - 2836 * hi;
	if (t <= 0)
		t += 0x7fffffff;
	ci->ci_randseed = t;
	return (t);
}