From 84adefa331c4159d432d22840663c38f155cd4c1 Mon Sep 17 00:00:00 2001
From: Erlang/OTP <otp@erlang.org>
Date: Fri, 20 Nov 2009 14:54:40 +0000
Subject: The R13B03 release.

---
 lib/erl_interface/src/registry/hash_isprime.c | 57 +++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 lib/erl_interface/src/registry/hash_isprime.c

(limited to 'lib/erl_interface/src/registry/hash_isprime.c')

diff --git a/lib/erl_interface/src/registry/hash_isprime.c b/lib/erl_interface/src/registry/hash_isprime.c
new file mode 100644
index 0000000000..cdef2591ab
--- /dev/null
+++ b/lib/erl_interface/src/registry/hash_isprime.c
@@ -0,0 +1,57 @@
+/*
+ * %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));
+}
-- 
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