rand.c (3130B)
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 36 #include <sys/types.h> 37 #include <stdlib.h> 38 39 typedef unsigned long u_long; 40 typedef unsigned int u_int; 41 42 static int 43 do_rand(unsigned long *ctx) 44 { 45 #ifdef USE_WEAK_SEEDING 46 /* 47 * Historic implementation compatibility. 48 * The random sequences do not vary much with the seed, 49 * even with overflowing. 50 */ 51 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 52 #else /* !USE_WEAK_SEEDING */ 53 /* 54 * Compute x = (7^5 * x) mod (2^31 - 1) 55 * wihout overflowing 31 bits: 56 * (2^31 - 1) = 127773 * (7^5) + 2836 57 * From "Random number generators: good ones are hard to find", 58 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 59 * October 1988, p. 1195. 60 */ 61 long hi, lo, x; 62 63 /* Can't be initialized with 0, so use another value. */ 64 if (*ctx == 0) 65 *ctx = 123459876; 66 hi = *ctx / 127773; 67 lo = *ctx % 127773; 68 x = 16807 * lo - 2836 * hi; 69 if (x < 0) 70 x += 0x7fffffff; 71 return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 72 #endif /* !USE_WEAK_SEEDING */ 73 } 74 75 76 int 77 rand_r(unsigned int *ctx) 78 { 79 u_long val = (u_long) *ctx; 80 int r = do_rand(&val); 81 82 *ctx = (unsigned int) val; 83 return (r); 84 } 85 86 static u_long next = 1; 87 88 int 89 rand() 90 { 91 return (do_rand(&next)); 92 } 93 94 void 95 srand(seed) 96 u_int seed; 97 { 98 next = seed; 99 } 100