Annotation of prex-old/usr/lib/libc/stdlib/random.c, Revision 1.1
1.1 ! nbrk 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: #include <sys/types.h>
! 34: #include <stdlib.h>
! 35:
! 36: #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
! 37:
! 38: static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
! 39:
! 40: void
! 41: srandom(seed)
! 42: u_long seed;
! 43: {
! 44: int i;
! 45:
! 46: randseed = seed;
! 47: for (i = 0; i < NSHUFF; i++)
! 48: (void)random();
! 49: }
! 50:
! 51: /*
! 52: * Pseudo-random number generator for randomizing the profiling clock,
! 53: * and whatever else we might use it for. The result is uniform on
! 54: * [0, 2^31 - 1].
! 55: */
! 56: long
! 57: random()
! 58: {
! 59: long x, hi, lo, t;
! 60:
! 61: /*
! 62: * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
! 63: * From "Random number generators: good ones are hard to find",
! 64: * Park and Miller, Communications of the ACM, vol. 31, no. 10,
! 65: * October 1988, p. 1195.
! 66: */
! 67: /* Can't be initialized with 0, so use another value. */
! 68: if ((x = randseed) == 0)
! 69: x = 123459876;
! 70: hi = x / 127773;
! 71: lo = x % 127773;
! 72: t = 16807 * lo - 2836 * hi;
! 73: if (t < 0)
! 74: t += 0x7fffffff;
! 75: randseed = t;
! 76: return (t);
! 77: }
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