1 files changed, 61 insertions, 0 deletions
diff --git a/src/base/intmath.cc b/src/base/intmath.cc
new file mode 100644
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--- /dev/null
+++ b/src/base/intmath.cc
@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2001, 2003-2005 The Regents of The University of Michigan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Nathan Binkert
+ *          Steve Reinhardt
+ */
+
+#include "base/intmath.hh"
+
+int
+prevPrime(int n)
+{
+    int decr;
+
+    // If the number is even, let's start with the previous odd number.
+    if (!(n & 1))
+        --n;
+
+    // Lets test for divisibility by 3.  Then we will be able to easily
+    // avoid numbers that are divisible by 3 in the future.
+    decr = n % 3;
+    if (decr == 0) {
+        n -= 2;
+        decr = 2;
+    }
+    else if (decr == 1)
+        decr = 4;
+
+    for (;;) {
+        if (isPrime(n))
+            return n;
+        n -= decr;
+        // Toggle between 2 and 4 to prevent trying numbers that are known
+        // to be divisible by 3.
+        decr = 6 - decr;
+    }
+}