53 lines
1.7 KiB
C++
53 lines
1.7 KiB
C++
/**
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* @file llmodularmath.h
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* @brief Useful modular math functions.
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*
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* $LicenseInfo:firstyear=2008&license=viewerlgpl$
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* Second Life Viewer Source Code
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* Copyright (C) 2010, Linden Research, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation;
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* version 2.1 of the License only.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*
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* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
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* $/LicenseInfo$
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*/
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#ifndef LLMODULARMATH_H
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#define LLMODULARMATH_H
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namespace LLModularMath
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{
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// Return difference between lhs and rhs
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// treating the U32 operands and result
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// as unsigned values of given width.
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template<int width>
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inline U32 subtract(U32 lhs, U32 rhs)
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{
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// Generate a bit mask which will truncate
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// unsigned values to given width at compile time.
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const U32 mask = (1 << width) - 1;
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// Operands are unsigned, so modular
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// arithmetic applies. If lhs < rhs,
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// difference will wrap in to lower
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// bits of result, which is then masked
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// to give a value that can be represented
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// by an unsigned value of width bits.
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return mask & (lhs - rhs);
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}
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}
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#endif
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