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39
40#ifndef HUFFMAN_P_H
41#define HUFFMAN_P_H
42
43//
44// W A R N I N G
45// -------------
46//
47// This file is not part of the Qt API. It exists for the convenience
48// of other Qt classes. This header file may change from version to
49// version without notice, or even be removed.
50//
51// We mean it.
52//
53
54#include <QtCore/qglobal.h>
55
56QT_BEGIN_NAMESPACE
57
58class QByteArray;
59
60namespace HPack
61{
62
63struct CodeEntry
64{
65 quint32 byteValue;
66 quint32 huffmanCode;
67 quint32 bitLength;
68};
69
70class BitOStream;
71
72quint64 huffman_encoded_bit_length(const QByteArray &inputData);
73void huffman_encode_string(const QByteArray &inputData, BitOStream &outputStream);
74
75// PrefixTable:
76// Huffman codes with a small bit length
77// fit into a table (these are 'terminal' symbols),
78// codes with longer codes require additional
79// tables, so several symbols will have the same index
80// in a table - pointing into the next table.
81// Every table has an 'indexLength' - that's
82// how many bits can fit in table's indices +
83// 'prefixLength' - how many bits were addressed
84// by its 'parent' table(s).
85// All PrefixTables are kept in 'prefixTables' array.
86// PrefixTable itself does not have any entries,
87// it just holds table's prefix/index + 'offset' -
88// there table's data starts in an array of all
89// possible entries ('tableData').
90
91struct PrefixTable
92{
93 PrefixTable()
94 : prefixLength(),
95 indexLength(),
96 offset()
97 {
98 }
99
100 PrefixTable(quint32 prefix, quint32 index)
101 : prefixLength(prefix),
102 indexLength(index),
103 offset()
104 {
105 }
106
107 quint32 size()const
108 {
109 // Number of entries table contains:
110 return 1 << indexLength;
111 }
112
113 quint32 prefixLength;
114 quint32 indexLength;
115 quint32 offset;
116};
117
118// Table entry is either a terminal entry (thus probably the code found)
119// or points into another table ('nextTable' - index into
120// 'prefixTables' array). If it's a terminal, 'nextTable' index
121// refers to the same table.
122
123struct PrefixTableEntry
124{
125 PrefixTableEntry()
126 : bitLength(),
127 nextTable(),
128 byteValue()
129 {
130 }
131
132 quint32 bitLength;
133 quint32 nextTable;
134 quint32 byteValue;
135};
136
137class BitIStream;
138
139class HuffmanDecoder
140{
141public:
142 enum class BitConstants
143 {
144 rootPrefix = 9,
145 childPrefix = 6
146 };
147
148 HuffmanDecoder();
149
150 bool decodeStream(BitIStream &inputStream, QByteArray &outputBuffer);
151
152private:
153 quint32 addTable(quint32 prefixLength, quint32 indexLength);
154 PrefixTableEntry tableEntry(const PrefixTable &table, quint32 index);
155 void setTableEntry(const PrefixTable &table, quint32 index, const PrefixTableEntry &entry);
156
157 std::vector<PrefixTable> prefixTables;
158 std::vector<PrefixTableEntry> tableData;
159 quint32 minCodeLength;
160};
161
162bool huffman_decode_string(BitIStream &inputStream, QByteArray *outputBuffer);
163
164} // namespace HPack
165
166QT_END_NAMESPACE
167
168#endif
169
170