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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** 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, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.1, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
**
**
**
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
//
// 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_HEADER
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 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
QT_END_HEADER
#endif
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