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 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)random.c 8.1 (Berkeley) 6/10/93 34 * $FreeBSD$ 35 */ 36 37 #include <sys/libkern.h> 38 39 #define NSHUFF 100 /* to drop part of seed -> 1st value correlation */ 40 41 static u_long randseed = 892053144; /* after srandom(1), NSHUFF counted */ 42 43 void 44 srandom(seed) 45 u_long seed; 46 { 47 int i; 48 49 randseed = seed; 50 for (i = 0; i < NSHUFF; i++) 51 (void)random(); 52 } 53 54 /* 55 * Pseudo-random number generator for randomizing the profiling clock, 56 * and whatever else we might use it for. The result is uniform on 57 * [0, 2^31 - 1]. 58 */ 59 u_long 60 random() 61 { 62 register long x, hi, lo, t; 63 64 /* 65 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 66 * From "Random number generators: good ones are hard to find", 67 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 68 * October 1988, p. 1195. 69 */ 70 /* Can't be initialized with 0, so use another value. */ 71 if ((x = randseed) == 0) 72 x = 123459876; 73 hi = x / 127773; 74 lo = x % 127773; 75 t = 16807 * lo - 2836 * hi; 76 if (t < 0) 77 t += 0x7fffffff; 78 randseed = t; 79 return (t); 80 } 81