lib: add rand() function

It's a PRNG using the simple and fast xorshift method.

Signed-off-by: Michael Walle <michael@walle.cc>
Cc: Wolfgang Denk <wd@denx.de>

lib/rand.c

@@ -0,0 +1,48 @@
+/*
+ * Simple xorshift PRNG
+ *   see http://www.jstatsoft.org/v08/i14/paper
+ *
+ * Copyright (c) 2012 Michael Walle
+ * Michael Walle <michael@walle.cc>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <common.h>
+
+static unsigned int y = 1U;
+
+unsigned int rand_r(unsigned int *seedp)
+{
+	*seedp ^= (*seedp << 13);
+	*seedp ^= (*seedp >> 17);
+	*seedp ^= (*seedp << 5);
+
+	return *seedp;
+}
+
+unsigned int rand(void)
+{
+	return rand_r(&y);
+}
+
+void srand(unsigned int seed)
+{
+	y = seed;
+}