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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#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/private/qglobal_p.h>
QT_BEGIN_NAMESPACE
class QByteArray;
namespace HPack
{
struct CodeEntry
{
quint32 byteValue;
quint32 huffmanCode;
quint32 bitLength;
};
class BitOStream;
quint64 huffman_encoded_bit_length(QByteArrayView inputData);
void huffman_encode_string(QByteArrayView 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
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