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+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef HUFFMAN_P_H
+#define HUFFMAN_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists for the convenience
+// of other Qt classes.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+class QByteArray;
+
+namespace HPack
+{
+
+struct CodeEntry
+{
+    CodeEntry() : byteValue(),
+                  huffmanCode(),
+                  bitLength()
+    {
+    }
+
+    CodeEntry(quint32 val, quint32 code, quint32 len)
+        : byteValue(val),
+          huffmanCode(code),
+          bitLength(len)
+    {
+    }
+
+    quint32 byteValue;
+    quint32 huffmanCode;
+    quint32 bitLength;
+};
+
+class BitOStream;
+
+quint64 huffman_encoded_bit_length(const QByteArray &inputData);
+void huffman_encode_string(const QByteArray &inputData, BitOStream &outputStream);
+
+// PrefixTable:
+// Huffman codes with a small bit length
+// fit into a table (these are 'terminal' symbols),
+// codes with longer codes require additional
+// tables, so several symbols will have the same index
+// in a table - pointing into the next table.
+// Every table has an 'indexLength' - that's
+// how many bits can fit in table's indices +
+// 'prefixLength' - how many bits were addressed
+// by its 'parent' table(s).
+// All PrefixTables are kept in 'prefixTables' array.
+// PrefixTable itself does not have any entries,
+// it just holds table's prefix/index + 'offset' -
+// there table's data starts in an array of all
+// possible entries ('tableData').
+
+struct PrefixTable
+{
+    PrefixTable()
+        : prefixLength(),
+          indexLength(),
+          offset()
+    {
+    }
+
+    PrefixTable(quint32 prefix, quint32 index)
+        : prefixLength(prefix),
+          indexLength(index),
+          offset()
+    {
+    }
+
+    quint32 size()const
+    {
+        // Number of entries table contains:
+        return 1 << indexLength;
+    }
+
+    quint32 prefixLength;
+    quint32 indexLength;
+    quint32 offset;
+};
+
+// Table entry is either a terminal entry (thus probably the code found)
+// or points into another table ('nextTable' - index into
+// 'prefixTables' array). If it's a terminal, 'nextTable' index
+// refers to the same table.
+
+struct PrefixTableEntry
+{
+    PrefixTableEntry()
+        : bitLength(),
+          nextTable(),
+          byteValue()
+    {
+    }
+
+    quint32 bitLength;
+    quint32 nextTable;
+    quint32 byteValue;
+};
+
+class BitIStream;
+
+class HuffmanDecoder
+{
+public:
+    enum class BitConstants
+    {
+        rootPrefix = 9,
+        childPrefix = 6
+    };
+
+    HuffmanDecoder();
+
+    bool decodeStream(BitIStream &inputStream, QByteArray &outputBuffer);
+
+private:
+    quint32 addTable(quint32 prefixLength, quint32 indexLength);
+    PrefixTableEntry tableEntry(const PrefixTable &table, quint32 index);
+    void setTableEntry(const PrefixTable &table, quint32 index, const PrefixTableEntry &entry);
+
+    std::vector<PrefixTable> prefixTables;
+    std::vector<PrefixTableEntry> tableData;
+    quint32 minCodeLength;
+};
+
+bool huffman_decode_string(BitIStream &inputStream, QByteArray *outputBuffer);
+
+} // namespace HPack
+
+QT_END_NAMESPACE
+
+#endif
+