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** General Public License version 2.1 as published by the Free Software

** Foundation and appearing in the file LICENSE.LGPL included in the

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//

//  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