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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_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 |