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authorErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
committerErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
commit84adefa331c4159d432d22840663c38f155cd4c1 (patch)
treebff9a9c66adda4df2106dfd0e5c053ab182a12bd /lib/erl_interface/src/registry/hash_isprime.c
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The R13B03 release.OTP_R13B03
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diff --git a/lib/erl_interface/src/registry/hash_isprime.c b/lib/erl_interface/src/registry/hash_isprime.c
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+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 1998-2009. All Rights Reserved.
+ *
+ * The contents of this file are subject to the Erlang Public License,
+ * Version 1.1, (the "License"); you may not use this file except in
+ * compliance with the License. You should have received a copy of the
+ * Erlang Public License along with this software. If not, it can be
+ * retrieved online at http://www.erlang.org/.
+ *
+ * Software distributed under the License is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ * the License for the specific language governing rights and limitations
+ * under the License.
+ *
+ * %CopyrightEnd%
+ *
+
+ */
+#include "hash.h"
+
+/* this is a general prime factoring function
+ * we get one prime factor each time we call it
+ * we only use it here to determine if n is prime,
+ * by checking if factor(n) == n .
+ */
+static int factor(int n)
+{
+ /* FIXME problem for threaded?! */
+ static int a[] = { 0, 4, 1, 2, 0, 2 };
+ static int m = 0;
+ static int d = 0;
+
+ if (n) {
+ m = n;
+ d = 2;
+ }
+
+ while ((d*d) <= m) {
+ if (!(m%d)) {
+ m /= d;
+ return d;
+ }
+ d += a[d%6];
+ }
+ n = m;
+ m = 0;
+
+ return n;
+}
+
+/* true if n prime */
+int ei_isprime(int n)
+{
+ return (n == factor(n));
+}