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+/** 
+ * @file llmodularmath.h
+ * @brief Useful modular math functions.
+ *
+ * $LicenseInfo:firstyear=2008&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2010, Linden Research, Inc.
+ * 
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ * 
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ * 
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#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