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diff --git a/quazip/quachecksum32.h b/quazip/quachecksum32.h
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+#ifndef QUACHECKSUM32_H
+#define QUACHECKSUM32_H
+
+#include <QtCore/QByteArray>
+#include "quazip_global.h"
+
+/// Checksum interface.
+/** \class QuaChecksum32 quachecksum32.h <quazip/quachecksum32.h>
+ * This is an interface for 32 bit checksums.
+ * Classes implementing this interface can calcunate a certin
+ * checksum in a single step:
+ * \code
+ * QChecksum32 *crc32 = new QuaCrc32(); 
+ * rasoult = crc32->calculate(data);
+ * \endcode
+ * or by streaming the data:
+ * \code
+ * QChecksum32 *crc32 = new QuaCrc32(); 
+ * while(!fileA.atEnd())
+ *     crc32->update(fileA.read(bufSize));
+ * resoultA = crc32->value();
+ * crc32->reset();
+ * while(!fileB.atEnd())
+ *     crc32->update(fileB.read(bufSize));
+ * resoultB = crc32->value();
+ * \endcode
+ */
+class QUAZIP_EXPORT QuaChecksum32
+{
+
+public:
+	///Calculates the checksum for data.
+	/** \a data source data
+	 * \return data checksum
+	 *
+	 * This function has no efect on the value returned by value().
+	 */
+	virtual quint32 calculate(const QByteArray &data) = 0;
+
+	///Resets the calculation on a checksun for a stream.
+	virtual void reset() = 0;
+
+	///Updates the calculated checksum for the stream
+	/** \a buf next portion of data from the stream
+	 */
+	virtual void update(const QByteArray &buf) = 0;
+
+	///Value of the checksum calculated for the stream passed throw update().
+	/** \return checksum
+	 */
+	virtual quint32 value() = 0;
+};
+
+#endif //QUACHECKSUM32_H