/** * @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