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include/raknet/DS_HuffmanEncodingTree.hpp

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+/*
+ *  Copyright (c) 2014, Oculus VR, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant 
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+/// \file DS_HuffmanEncodingTree.h
+/// \brief \b [Internal] Generates a huffman encoding tree, used for string and global compression.
+///
+
+
+#ifndef __HUFFMAN_ENCODING_TREE
+#define __HUFFMAN_ENCODING_TREE
+
+#include "RakMemoryOverride.hpp"
+#include "DS_HuffmanEncodingTreeNode.hpp"
+#include "BitStream.hpp"
+#include "Export.hpp"
+#include "DS_LinkedList.hpp" 
+
+namespace RakNet
+{
+
+/// This generates special cases of the huffman encoding tree using 8 bit keys with the additional condition that unused combinations of 8 bits are treated as a frequency of 1
+class RAK_DLL_EXPORT HuffmanEncodingTree
+{
+
+public:
+	HuffmanEncodingTree();
+	~HuffmanEncodingTree();
+
+	/// \brief Pass an array of bytes to array and a preallocated BitStream to receive the output.
+	/// \param [in] input Array of bytes to encode
+	/// \param [in] sizeInBytes size of \a input
+	/// \param [out] output The bitstream to write to
+	void EncodeArray( unsigned char *input, size_t sizeInBytes, RakNet::BitStream * output );
+
+	// \brief Decodes an array encoded by EncodeArray().
+	unsigned DecodeArray( RakNet::BitStream * input, BitSize_t sizeInBits, size_t maxCharsToWrite, unsigned char *output );
+	void DecodeArray( unsigned char *input, BitSize_t sizeInBits, RakNet::BitStream * output );
+
+	/// \brief Given a frequency table of 256 elements, all with a frequency of 1 or more, generate the tree.
+	void GenerateFromFrequencyTable( unsigned int frequencyTable[ 256 ] );
+
+	/// \brief Free the memory used by the tree.
+	void FreeMemory( void );
+
+private:
+
+	/// The root node of the tree 
+
+	HuffmanEncodingTreeNode *root;
+
+	/// Used to hold bit encoding for one character
+
+
+	struct CharacterEncoding
+	{
+		unsigned char* encoding;
+		unsigned short bitLength;
+	};
+
+	CharacterEncoding encodingTable[ 256 ];
+
+	void InsertNodeIntoSortedList( HuffmanEncodingTreeNode * node, DataStructures::LinkedList<HuffmanEncodingTreeNode *> *huffmanEncodingTreeNodeList ) const;
+};
+
+} // namespace RakNet
+
+#endif