154353Storek /*-
2*63186Sbostic * Copyright (c) 1992, 1993
3*63186Sbostic * The Regents of the University of California. All rights reserved.
454353Storek *
554353Storek * %sccs.include.redist.c%
654353Storek *
7*63186Sbostic * @(#)random.c 8.1 (Berkeley) 06/10/93
854353Storek */
954353Storek
1056518Sbostic #include <libkern/libkern.h>
1154353Storek
1254353Storek /*
1354353Storek * Pseudo-random number generator for randomizing the profiling clock,
1454353Storek * and whatever else we might use it for. The result is uniform on
1554353Storek * [0, 2^31 - 1].
1654353Storek */
1754353Storek u_long
random()1854353Storek random()
1954353Storek {
2054353Storek static u_long randseed = 1;
2154353Storek register long x, hi, lo, t;
2254353Storek
2354353Storek /*
2454353Storek * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
2554353Storek * From "Random number generators: good ones are hard to find",
2654353Storek * Park and Miller, Communications of the ACM, vol. 31, no. 10,
2754353Storek * October 1988, p. 1195.
2854353Storek */
2954353Storek x = randseed;
3054353Storek hi = x / 127773;
3154353Storek lo = x % 127773;
3254353Storek t = 16807 * lo - 2836 * hi;
3354353Storek if (t <= 0)
3454353Storek t += 0x7fffffff;
3554353Storek randseed = t;
3654353Storek return (t);
3754353Storek }
38