date and time created 92/06/24 01:08:54 by torek

SCCS-vsn: sys/libkern/random.c 7.1

diff --git a/usr/src/sys/libkern/random.c b/usr/src/sys/libkern/random.c
new file mode 100644 (file)
index 0000000..6c25d70
--- /dev/null
+++ b/usr/src/sys/libkern/random.c
@@ -0,0 +1,37 @@
+/*-
+ * Copyright (c) 1992 The Regents of the University of California.
+ * All rights reserved.
+ *
+ * %sccs.include.redist.c%
+ *
+ *     @(#)random.c    7.1 (Berkeley) %G%
+ */
+
+#include "libkern.h"
+
+/*
+ * Pseudo-random number generator for randomizing the profiling clock,
+ * and whatever else we might use it for.  The result is uniform on
+ * [0, 2^31 - 1].
+ */
+u_long
+random()
+{
+       static u_long randseed = 1;
+       register long x, hi, lo, t;
+
+       /*
+        * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
+        * From "Random number generators: good ones are hard to find",
+        * Park and Miller, Communications of the ACM, vol. 31, no. 10,
+        * October 1988, p. 1195.
+        */
+       x = randseed;
+       hi = x / 127773;
+       lo = x % 127773;
+       t = 16807 * lo - 2836 * hi;
+       if (t <= 0)
+               t += 0x7fffffff;
+       randseed = t;
+       return (t);
+}