Release calc version 2.10.2t30

lib/mersenne.cal

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 1995 David I. Bell
+ * Permission is granted to use, distribute, or modify this source,
+ * provided that this copyright notice remains intact.
+ *
+ * Perform a primality test of 2^p-1, for prime p>1.
+ */
+
+define mersenne(p)
+{
+	local u, i, p_mask;
+
+	/* firewall */
+	if (! isint(p))
+		quit "p is not an integer";
+
+	/* two is a special case */
+	if (p == 2)
+		return 1;
+
+	/* if p is not prime, then 2^p-1 is not prime */
+	if (! ptest(p,10))
+		return 0;
+
+	/* calculate 2^p-1 for later mods */
+	p_mask = 2^p - 1;
+
+	/* lltest: u(i+1) = u(i)^2 - 2 mod 2^p-1 */
+	u = 4;
+	for (i = 2; i < p; ++i) {
+		u = u^2 - 2;
+		u = u&p_mask + u>>p;
+		if (u > p_mask)
+			u = u&p_mask + 1;
+	}
+
+	/* 2^p-1 is prime iff u(p) = 0 mod 2^p-1 */
+	return (u == p_mask);
+}
+
+global lib_debug;
+if (lib_debug >= 0) {
+    print "mersenne(p) defined";
+}