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/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtXmlPatterns 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 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 Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 or 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.GPL2 and 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-2.0.html and
** https://www.gnu.org/licenses/gpl-3.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/
//
// 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.
#ifndef Patternist_CompressedWhitespace_H
#define Patternist_CompressedWhitespace_H
#include <QtGlobal>
QT_BEGIN_NAMESPACE
class QChar;
class QString;
class QStringRef;
namespace QPatternist
{
/**
* @short A compression facility for whitespace nodes.
*
* CompressedWhitespace compresses and decompresses strings that consists of
* whitespace only, and do so with a scheme that is designed to do this
* specialized task in an efficient way. The approach is simple: each
* sequence of equal whitespace in the input gets coded into one byte,
* where the first two bits signals the type, CharIdentifier, and the
* remininding six bits is the count.
*
* For instance, this scheme manages to compress a sequence of spaces
* followed by a new line into 16 bits(one QChar), and QString stores
* strings of one QChar quite efficiently, by avoiding a heap allocation.
*
* There is no way to tell whether a QString is compressed or not.
*
* The compression scheme originates from Saxon, by Michael Kay.
*
* @author Frans Englich <frans.englich@nokia.com>
*/
class Q_AUTOTEST_EXPORT CompressedWhitespace
{
public:
/**
* @short Compresses @p input into a compressed format, returned
* as a QString.
*
* The caller guarantees that input is not empty
* and consists only of whitespace.
*
* The returned format is opaque. There is no way to find out
* whether a QString contains compressed data or not.
*
* @see decompress()
*/
static QString compress(const QStringRef &input);
/**
* @short Decompresses @p input into a usual QString.
*
* @p input must be a QString as per returned from compress().
*
* @see compress()
*/
static QString decompress(const QString &input);
private:
/**
* We use the two upper bits for communicating what space it is.
*/
enum CharIdentifier
{
Space = 0x0,
/**
* 0xA, \\r
*
* Binary: 10000000
*/
CR = 0x80,
/**
* 0xD, \\n
*
* Binary: 01000000
*/
LF = 0x40,
/**
* Binary: 11000000
*/
Tab = 0xC0
};
enum Constants
{
/* We can at maximum store this many consecutive characters
* of one type. We use 6 bits for the count. */
MaxCharCount = (1 << 6) - 1,
/**
* Binary: 11111111
*/
Lower8Bits = (1 << 8) - 1,
/**
* Binary: 111111
*/
Lower6Bits = (1 << 6) - 1,
/*
* Binary: 11000000
*/
UpperTwoBits = 3 << 6
};
static inline CharIdentifier toIdentifier(const QChar ch);
static inline quint8 toCompressedChar(const QChar ch, const int len);
static inline QChar toChar(const CharIdentifier id);
/**
* @short Returns @c true if @p number is an even number, otherwise
* @c false.
*/
static inline bool isEven(const int number);
/**
* @short This class can only be used via its static members.
*/
inline CompressedWhitespace();
Q_DISABLE_COPY(CompressedWhitespace)
};
}
QT_END_NAMESPACE
#endif
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