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+/** 
+ * @file llmodularmath.h
+ * @brief Useful modular math functions.
+ *
+ * $LicenseInfo:firstyear=2008&license=viewergpl$
+ * 
+ * Copyright (c) 2008, Linden Research, Inc.
+ * 
+ * Second Life Viewer Source Code
+ * The source code in this file ("Source Code") is provided by Linden Lab
+ * to you under the terms of the GNU General Public License, version 2.0
+ * ("GPL"), unless you have obtained a separate licensing agreement
+ * ("Other License"), formally executed by you and Linden Lab.  Terms of
+ * the GPL can be found in doc/GPL-license.txt in this distribution, or
+ * online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
+ * 
+ * There are special exceptions to the terms and conditions of the GPL as
+ * it is applied to this Source Code. View the full text of the exception
+ * in the file doc/FLOSS-exception.txt in this software distribution, or
+ * online at http://secondlifegrid.net/programs/open_source/licensing/flossexception
+ * 
+ * By copying, modifying or distributing this software, you acknowledge
+ * that you have read and understood your obligations described above,
+ * and agree to abide by those obligations.
+ * 
+ * ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
+ * WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
+ * COMPLETENESS OR PERFORMANCE.
+ * $/LicenseInfo$
+ */
+
+#ifndef LLMODULARMATH_H
+#define LLMODULARMATH_H
+
+namespace LLModularMath
+{
+    // Return difference between lhs and rhs
+    // treating the U32 operands and result
+    // as unsigned values of given width.
+        template<int width>
+        inline U32 subtract(U32 lhs, U32 rhs)
+        {
+                // Generate a bit mask which will truncate
+                // unsigned values to given width at compile time.
+                const U32 mask = (1 << width) - 1;
+                
+                // Operands are unsigned, so modular
+                // arithmetic applies. If lhs < rhs,
+                // difference will wrap in to lower
+                // bits of result, which is then masked
+                // to give a value that can be represented
+                // by an unsigned value of width bits.
+                return mask & (lhs - rhs);
+        }       
+}
+
+#endif