1 files changed, 81 insertions, 0 deletions
diff --git a/include/clplumbing/cl_random.h b/include/clplumbing/cl_random.h
new file mode 100644
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+++ b/include/clplumbing/cl_random.h
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+
+/*							
+ * Copyright (C) 2005 Guochun Shi <gshi@ncsa.uiuc.edu>
+ * Copyright (C) 2005 International Business Machines Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include <stdlib.h>
+
+/* Intended usage is srand(cl_randseed()).
+ * This returns on "as good as it gets" random number usually taken from
+ * /dev/urandom to have a nice seed for future random numbers generated by
+ * rand(). */
+unsigned int	cl_randseed(void);
+
+/* get_next_random() currently rand() based.
+ *
+ * You probably want to use cl_rand_from_interval instead.
+ *
+ * You don't need to srand(), it will seed once with cl_randseed internally.
+ *
+ * It is called that way, because it was exposed in the header file for a long
+ * time, and used to be coded in an attempt to pregenerate a queue of random
+ * numbers from the mainloop, and it would shift the next random number from
+ * that queue and trigger generation of new random numbers "at idle time" to
+ * refill that queue.
+ * Only that functionality never actually worked, is not interessting anymore
+ * anyways (rand() is cheap enough), and is now ripped out.
+ *
+ * So it now does srand(cl_randseed()) once internally,
+ * and from there on is equivalent to calling rand() directly,
+ * and could be called cl_rand().
+ *
+ * If you want your own specific rand seed to re-generate a particular
+ * sequence, call it once, throw away the return code, then call
+ * srand(yourseed).  Or don't use it anywhere in your code. */
+int		get_next_random(void);
+
+/* generate some random number in the range [a;b];
+ * typically used to randomly delay messages. */
+#define HAVE_CL_RAND_FROM_INTERVAL 1
+static inline
+int		cl_rand_from_interval(const int a, const int b)
+{
+	/*
+	 * Be careful here, you don't know RAND_MAX at coding time,
+	 * only at compile time. If you think
+	 *   (int)(a + (rand()*(b-a)+(RAND_MAX/2))/RAND_MAX);
+	 * was correct, think again with RAND_MAX = INT_MAX,
+	 * which is the case for many rand() implementations nowadays.
+	 *
+	 * Don't do modulo, either, as that will skew the distribution, and
+	 * still has possible wraparounds, or an insufficient input set for too
+	 * small RAND_MAX.
+	 *
+	 * Rather do the whole calculation in 64 bit, which should be correct
+	 * as long as r, a, b, and RAND_MAX are all int.
+	 * Of course, if you prefer, you can do it with floating point as well.
+	 */
+#if 1		/* use long long */
+	long long r = get_next_random();
+	r = a + (r * (b-a) + RAND_MAX/2)/RAND_MAX;
+#else		/* use floating point */
+	int r = get_next_random();
+	r = a + (int)(1.0 / RAND_MAX * r * (b-a) + 0.5);
+#endif
+	return r;
+}