diff options
Diffstat (limited to 'src/v8/qcalculatehash_p.h')
-rw-r--r-- | src/v8/qcalculatehash_p.h | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/src/v8/qcalculatehash_p.h b/src/v8/qcalculatehash_p.h new file mode 100644 index 0000000..715fa6e --- /dev/null +++ b/src/v8/qcalculatehash_p.h @@ -0,0 +1,140 @@ +/**************************************************************************** +** +** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies). +** Contact: http://www.qt-project.org/legal +** +** This file is part of the QtV8 module of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:LGPL$ +** 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 Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/contact-us. +** +** GNU Lesser General Public License Usage +** Alternatively, this file may be used under the terms of the GNU Lesser +** General Public License version 2.1 as published by the Free Software +** Foundation and appearing in the file LICENSE.LGPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU Lesser General Public License version 2.1 requirements +** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. +** +** In addition, as a special exception, Digia gives you certain additional +** rights. These rights are described in the Digia Qt LGPL Exception +** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. +** +** GNU General Public License Usage +** Alternatively, this file may be used under the terms of the GNU +** General Public License version 3.0 as published by the Free Software +** Foundation and appearing in the file LICENSE.GPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU General Public License version 3.0 requirements will be +** met: http://www.gnu.org/copyleft/gpl.html. +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +#ifndef CALCULATEHASH_P_H +#define CALCULATEHASH_P_H + +// +// W A R N I N G +// ------------- +// +// This file is not part of the Qt API. It exists purely as an +// implementation detail. This header file may change from version to +// version without notice, or even be removed. +// +// We mean it. +// + +#include <QtCore/qglobal.h> +#include <QtCore/qstring.h> + +QT_BEGIN_NAMESPACE + +// This is a reimplementation of V8's string hash algorithm. It is significantly +// faster to do it here than call into V8, but it adds the maintenance burden of +// ensuring that the two hashes are identical. We Q_ASSERT() that the two return +// the same value. If these asserts start to fail, the hash code needs to be +// synced with V8. +namespace HashedString { + static const int kMaxArrayIndexSize = 10; + static const int kMaxHashCalcLength = 16383; + static const int kNofHashBitFields = 2; + static const int kHashShift = kNofHashBitFields; + static const int kIsNotArrayIndexMask = 1 << 1; + static const int kArrayIndexValueBits = 24; + static const int kArrayIndexHashLengthShift = kArrayIndexValueBits + kNofHashBitFields; + static const int kMaxCachedArrayIndexLength = 7; +}; + +template <typename schar> +uint32_t calculateHash(const schar* chars, int length) { + if (length > HashedString::kMaxHashCalcLength) { + // V8 trivial hash + return (length << HashedString::kHashShift) | HashedString::kIsNotArrayIndexMask; + } + + uint32_t raw_running_hash = 0; + uint32_t array_index = 0; + bool is_array_index = (0 < length && length <= HashedString::kMaxArrayIndexSize); + bool is_first_char = true; + + int ii = 0; + for (;is_array_index && ii < length; ++ii) { + quint32 c = *chars++; + + raw_running_hash += c; + raw_running_hash += (raw_running_hash << 10); + raw_running_hash ^= (raw_running_hash >> 6); + + if (c < '0' || c > '9') { + is_array_index = false; + } else { + int d = c - '0'; + if (is_first_char) { + is_first_char = false; + if (c == '0' && length > 1) { + is_array_index = false; + continue; + } + } + if (array_index > 429496729U - ((d + 2) >> 3)) { + is_array_index = false; + } else { + array_index = array_index * 10 + d; + } + } + } + + for (;ii < length; ++ii) { + raw_running_hash += *chars++; + raw_running_hash += (raw_running_hash << 10); + raw_running_hash ^= (raw_running_hash >> 6); + } + + if (is_array_index) { + array_index <<= HashedString::kHashShift; + array_index |= length << HashedString::kArrayIndexHashLengthShift; + return array_index; + } else { + raw_running_hash += (raw_running_hash << 3); + raw_running_hash ^= (raw_running_hash >> 11); + raw_running_hash += (raw_running_hash << 15); + if (raw_running_hash == 0) { + raw_running_hash = 27; + } + + return (raw_running_hash << HashedString::kHashShift) | HashedString::kIsNotArrayIndexMask; + } +} + +QT_END_NAMESPACE + +#endif // CALCULATEHASH_P_H |