mirror of
https://github.com/crystalidea/qt6windows7.git
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57 lines
1.6 KiB
C++
57 lines
1.6 KiB
C++
// Copyright (C) 2016 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
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#include "tst_bench_qhash.h"
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QT_BEGIN_NAMESPACE
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size_t qHash(const Qt4String &str)
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{
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qsizetype n = str.size();
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const QChar *p = str.unicode();
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uint h = 0;
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while (n--) {
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h = (h << 4) + (*p++).unicode();
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h ^= (h & 0xf0000000) >> 23;
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h &= 0x0fffffff;
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}
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return h;
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}
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size_t qHash(const Qt50String &key, size_t seed)
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{
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const QChar *p = key.unicode();
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qsizetype len = key.size();
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size_t h = seed;
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for (int i = 0; i < len; ++i)
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h = 31 * h + p[i].unicode();
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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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size_t qHash(const JavaString &str)
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{
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const auto *p = reinterpret_cast<const char16_t *>(str.constData());
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const qsizetype 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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