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/**
* @file llmodularmath.h
* @brief Useful modular math functions.
*
* $LicenseInfo:firstyear=2008&license=viewergpl$
*
* Copyright (c) 2008-2009, 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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