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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
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