Annotation of sys/lib/libkern/random.c, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: random.c,v 1.7 2004/08/07 00:38:33 deraadt Exp $ */
! 2: /* $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $ */
! 3:
! 4: /*-
! 5: * Copyright (c) 1992, 1993
! 6: * The Regents of the University of California. All rights reserved.
! 7: *
! 8: * Redistribution and use in source and binary forms, with or without
! 9: * modification, are permitted provided that the following conditions
! 10: * are met:
! 11: * 1. Redistributions of source code must retain the above copyright
! 12: * notice, this list of conditions and the following disclaimer.
! 13: * 2. Redistributions in binary form must reproduce the above copyright
! 14: * notice, this list of conditions and the following disclaimer in the
! 15: * documentation and/or other materials provided with the distribution.
! 16: * 3. Neither the name of the University nor the names of its contributors
! 17: * may be used to endorse or promote products derived from this software
! 18: * without specific prior written permission.
! 19: *
! 20: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
! 21: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 22: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 23: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
! 24: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 25: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 26: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 27: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 28: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 29: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 30: * SUCH DAMAGE.
! 31: *
! 32: * @(#)random.c 8.1 (Berkeley) 6/10/93
! 33: */
! 34:
! 35: #include <sys/types.h>
! 36:
! 37: #include <lib/libkern/libkern.h>
! 38:
! 39: /*
! 40: * Pseudo-random number generator for randomizing the profiling clock,
! 41: * and whatever else we might use it for. The result is uniform on
! 42: * [0, 2^31 - 1].
! 43: */
! 44: u_long _randseed = 1;
! 45:
! 46: u_long
! 47: random(void)
! 48: {
! 49: long x, hi, lo, t;
! 50:
! 51: /*
! 52: * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
! 53: * From "Random number generators: good ones are hard to find",
! 54: * Park and Miller, Communications of the ACM, vol. 31, no. 10,
! 55: * October 1988, p. 1195.
! 56: */
! 57: x = _randseed;
! 58: hi = x / 127773;
! 59: lo = x % 127773;
! 60: t = 16807 * lo - 2836 * hi;
! 61: if (t <= 0)
! 62: t += 0x7fffffff;
! 63: _randseed = t;
! 64: return (t);
! 65: }
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