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/* $OpenBSD: random.c,v 1.9 2014/01/19 12:45:36 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 <sys/types.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);
}
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