1 /*- 2 * Copyright (c) 1992, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 4. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)random.c 8.1 (Berkeley) 6/10/93 30 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD$"); 34 35 #include <sys/libkern.h> 36 37 #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */ 38 39 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */ 40 41 void 42 srandom(seed) 43 u_long seed; 44 { 45 int i; 46 47 randseed = seed; 48 for (i = 0; i < NSHUFF; i++) 49 (void)random(); 50 } 51 52 /* 53 * Pseudo-random number generator for perturbing the profiling clock, 54 * and whatever else we might use it for. The result is uniform on 55 * [0, 2^31 - 1]. 56 */ 57 u_long 58 random() 59 { 60 long x, hi, lo, t; 61 62 /* 63 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 64 * From "Random number generators: good ones are hard to find", 65 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 66 * October 1988, p. 1195. 67 */ 68 /* Can't be initialized with 0, so use another value. */ 69 if ((x = randseed) == 0) 70 x = 123459876; 71 hi = x / 127773; 72 lo = x % 127773; 73 t = 16807 * lo - 2836 * hi; 74 if (t < 0) 75 t += 0x7fffffff; 76 randseed = t; 77 return (t); 78 } 79