115 lines
3.6 KiB
C++
115 lines
3.6 KiB
C++
/****************************************************************************
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**
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** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
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** Contact: http://www.qt-project.org/
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**
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** This file is part of the QtTest module of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** GNU Lesser General Public License Usage
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** This file may be used under the terms of the GNU Lesser General Public
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** License version 2.1 as published by the Free Software Foundation and
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** appearing in the file LICENSE.LGPL included in the packaging of this
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** file. Please review the following information to ensure the GNU Lesser
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** General Public License version 2.1 requirements will be met:
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** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Nokia gives you certain additional
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** rights. These rights are described in the Nokia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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** GNU General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU General
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** Public License version 3.0 as published by the Free Software Foundation
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** and appearing in the file LICENSE.GPL included in the packaging of this
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** file. Please review the following information to ensure the GNU General
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** Public License version 3.0 requirements will be met:
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** http://www.gnu.org/copyleft/gpl.html.
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**
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** Other Usage
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** Alternatively, this file may be used in accordance with the terms and
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** conditions contained in a signed written agreement between you and Nokia.
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**
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**
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**
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**
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#include "main.h"
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static void doHash(const unsigned short *p, uint &h)
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{
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#if 1
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// Copied from static uint hash(const QChar *p, int n).
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// Possibly not the cheapest way.
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h = (h << 4) + (*p++);
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h ^= (h & 0xf0000000) >> 23;
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h &= 0x0fffffff;
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h = (h << 4) + (*p++);
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h ^= (h & 0xf0000000) >> 23;
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h &= 0x0fffffff;
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h = (h << 4) + (*p++);
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h ^= (h & 0xf0000000) >> 23;
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h &= 0x0fffffff;
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h = (h << 4) + (*p++);
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h ^= (h & 0xf0000000) >> 23;
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h &= 0x0fffffff;
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#else
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// Faster, but probably less spread.
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h ^= *(unsigned int *)p;
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#endif
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}
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QT_BEGIN_NAMESPACE
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uint qHash(const String &str)
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{
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const unsigned short *p = (unsigned short *)str.constData();
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const int s = str.size();
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switch (s) {
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case 0: return 0;
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case 1: return *p;
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case 2: return *(unsigned int *)p;
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case 3: return (*(unsigned int *)p) ^ *(p + 2);
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//case 3: return (*p << 11) + (*(p + 1) << 22) + *(p + 2);
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}
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uint h = 0;
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doHash(p, h);
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doHash(p + s / 2 - 2, h);
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doHash(p + s - 4, h);
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return h;
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}
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// The Java's hashing algorithm for strings is a variation of D. J. Bernstein
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// hashing algorithm appeared here http://cr.yp.to/cdb/cdb.txt
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// and informally known as DJB33XX - DJB's 33 Times Xor.
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// Java uses DJB31XA, that is, 31 Times Add.
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// The original algorithm was a loop around "(h << 5) + h ^ c",
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// which is indeed "h * 33 ^ c"; it was then changed to
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// "(h << 5) - h ^ c", so "h * 31 ^ c", and the XOR changed to a sum:
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// "(h << 5) - h + c", which can save some assembly instructions.
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// Still, we can avoid writing the multiplication as "(h << 5) - h"
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// -- the compiler will turn it into a shift and an addition anyway
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// (for instance, gcc 4.4 does that even at -O0).
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uint qHash(const JavaString &str)
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{
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const unsigned short *p = (unsigned short *)str.constData();
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const int len = str.size();
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uint h = 0;
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for (int i = 0; i < len; ++i)
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h = 31 * h + p[i];
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return h;
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}
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QT_END_NAMESPACE
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