1 /*- 2 * Copyright (c) 1990, 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 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. 34 * 35 * $FreeBSD$ 36 */ 37 38 #if defined(LIBC_SCCS) && !defined(lint) 39 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; 40 #endif /* LIBC_SCCS and not lint */ 41 42 #include <sys/types.h> 43 #include <stdlib.h> 44 45 #ifdef TEST 46 #include <stdio.h> 47 #endif /* TEST */ 48 49 static int 50 do_rand(unsigned long *ctx) 51 { 52 #ifdef USE_WEAK_SEEDING 53 /* 54 * Historic implementation compatibility. 55 * The random sequences do not vary much with the seed, 56 * even with overflowing. 57 */ 58 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 59 #else /* !USE_WEAK_SEEDING */ 60 /* 61 * Compute x = (7^5 * x) mod (2^31 - 1) 62 * wihout overflowing 31 bits: 63 * (2^31 - 1) = 127773 * (7^5) + 2836 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 long hi, lo, x; 69 70 hi = *ctx / 127773; 71 lo = *ctx % 127773; 72 x = 16807 * lo - 2836 * hi; 73 if (x <= 0) 74 x += 0x7fffffff; 75 return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 76 #endif /* !USE_WEAK_SEEDING */ 77 } 78 79 80 int 81 rand_r(unsigned int *ctx) 82 { 83 u_long val = (u_long) *ctx; 84 *ctx = do_rand(&val); 85 return (int) *ctx; 86 } 87 88 89 static u_long next = 1; 90 91 int 92 rand() 93 { 94 return do_rand(&next); 95 } 96 97 void 98 srand(seed) 99 u_int seed; 100 { 101 next = seed; 102 } 103 104 #ifdef TEST 105 106 main() 107 { 108 int i; 109 unsigned myseed; 110 111 printf("seeding rand with 0x19610910: \n"); 112 srand(0x19610910); 113 114 printf("generating three pseudo-random numbers:\n"); 115 for (i = 0; i < 3; i++) 116 { 117 printf("next random number = %d\n", rand()); 118 } 119 120 printf("generating the same sequence with rand_r:\n"); 121 myseed = 0x19610910; 122 for (i = 0; i < 3; i++) 123 { 124 printf("next random number = %d\n", rand_r(&myseed)); 125 } 126 127 return 0; 128 } 129 130 #endif /* TEST */ 131 132