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Diffstat (limited to 'src/system/Qt3DSHash.h')
| -rw-r--r-- | src/system/Qt3DSHash.h | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/src/system/Qt3DSHash.h b/src/system/Qt3DSHash.h new file mode 100644 index 0000000..8baa2db --- /dev/null +++ b/src/system/Qt3DSHash.h @@ -0,0 +1,105 @@ +/**************************************************************************** +** +** Copyright (C) 1993-2009 NVIDIA Corporation. +** Copyright (C) 2017 The Qt Company Ltd. +** Contact: https://www.qt.io/licensing/ +** +** This file is part of Qt 3D Studio. +** +** $QT_BEGIN_LICENSE:GPL$ +** Commercial License Usage +** Licensees holding valid commercial Qt licenses may use this file in +** accordance with the commercial license agreement provided with the +** Software or, alternatively, in accordance with the terms contained in +** a written agreement between you and The Qt Company. For licensing terms +** and conditions see https://www.qt.io/terms-conditions. For further +** information use the contact form at https://www.qt.io/contact-us. +** +** GNU General Public License Usage +** Alternatively, this file may be used under the terms of the GNU +** General Public License version 3 or (at your option) any later version +** approved by the KDE Free Qt Foundation. The licenses are as published by +** the Free Software Foundation and appearing in the file LICENSE.GPL3 +** included in the packaging of this file. Please review the following +** information to ensure the GNU General Public License requirements will +** be met: https://www.gnu.org/licenses/gpl-3.0.html. +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +#pragma once +#include "Qt3DSConfig.h" + +//============================================================================== +// Namespace +//============================================================================== +namespace Q3DStudio { + +//============================================================================== +/** + * Utility class transforming a string into a hash value. + */ +class CHash +{ + //============================================================================== + // Methods + //============================================================================== +public: // Static utility + //============================================================================== + /** + * We use the hashing algorithm called "sdbm". + * + * This algorithm was created from sdbm (a public-domain reimplementation + * of ndbm) database library. It was found to do well in scrambling bits, + * causing better distribution of the keys and fewer splits. it also happens + * to be a good general hashing function with good distribution. the actual + * function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below + * is the faster version used in gawk. [there is even a faster, duff-device + * version] the magic constant 65599 was picked out of thin air while + * experimenting with different constants, and turns out to be a prime. this + * is one of the algorithms used in berkeley db (see sleepycat) and elsewhere. + * + * @param inString the string to hash + * @return the hash value + */ + static TStringHash HashString(const CHAR *inString) + { + TStringHash theHash = 0; + INT32 theChar = *inString; + INT32 theCount = 0; + while (theChar && (theCount < HASH_LIMIT)) { + theChar = *inString++; + theHash = theChar + (theHash << 6) + (theHash << 16) - theHash; + ++theCount; + } + + return theHash; + } + + //============================================================================== + /** + * 31-bit hash with MSB set to 0 + * + * @param inString the string to hash + * @return the 31-bit hash value + */ + static TEventCommandHash HashEventCommand(const CHAR *inString) + { + return HashString(inString) & 0x7fffffff; + } + + //============================================================================== + /** + * 26-bit hash with MSBs all set to 0 + * + * @param inString the string to hash + * @return the 26-bit hash value + */ + static TAttributeHash HashAttribute(const CHAR *inString) + { + return HashString(inString) & 0x03ffffff; + } +}; + +} // namespace Q3DStudio |