From 7abecb48babe6a6f09bf6692ba55076546cfced9 Mon Sep 17 00:00:00 2001
From: Jacek Antonelli
Date: Mon, 1 Dec 2008 17:39:58 -0600
Subject: Second Life viewer sources 1.22.0-RC

---
 linden/indra/llmath/llmodularmath.h | 57 +++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 linden/indra/llmath/llmodularmath.h

(limited to 'linden/indra/llmath/llmodularmath.h')

diff --git a/linden/indra/llmath/llmodularmath.h b/linden/indra/llmath/llmodularmath.h
new file mode 100644
index 0000000..076f5da
--- /dev/null
+++ b/linden/indra/llmath/llmodularmath.h
@@ -0,0 +1,57 @@
+/** 
+ * @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
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