/** * @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