C++ BitStream::CopyData方法代码示例

// Given a frequency table of 256 elements, all with a frequency of 1 or more, generate the tree
void HuffmanEncodingTree::GenerateFromFrequencyTable( unsigned int frequencyTable[ 256 ] )
{
	int counter;
	HuffmanEncodingTreeNode * node;
	HuffmanEncodingTreeNode *leafList[ 256 ]; // Keep a copy of the pointers to all the leaves so we can generate the encryption table bottom-up, which is easier
	// 1.  Make 256 trees each with a weight equal to the frequency of the corresponding character
	DataStructures::LinkedList<HuffmanEncodingTreeNode *> huffmanEncodingTreeNodeList;
	
	FreeMemory();
	
	for ( counter = 0; counter < 256; counter++ )
	{
		node = new HuffmanEncodingTreeNode;
		node->left = 0;
		node->right = 0;
		node->value = (unsigned char) counter;
		node->weight = frequencyTable[ counter ];
		
		if ( node->weight == 0 )
			node->weight = 1; // 0 weights are illegal
			
		leafList[ counter ] = node; // Used later to generate the encryption table
		
		InsertNodeIntoSortedList( node, &huffmanEncodingTreeNodeList ); // Insert and maintain sort order.
	}
	
	
	// 2.  While there is more than one tree, take the two smallest trees and merge them so that the two trees are the left and right
	// children of a new node, where the new node has the weight the sum of the weight of the left and right child nodes.
#ifdef _MSC_VER
#pragma warning( disable : 4127 ) // warning C4127: conditional expression is constant
#endif
	while ( 1 )
	{
		huffmanEncodingTreeNodeList.Beginning();
		HuffmanEncodingTreeNode *lesser, *greater;
		lesser = huffmanEncodingTreeNodeList.Pop();
		greater = huffmanEncodingTreeNodeList.Pop();
		node = new HuffmanEncodingTreeNode;
		node->left = lesser;
		node->right = greater;
		node->weight = lesser->weight + greater->weight;
		lesser->parent = node;  // This is done to make generating the encryption table easier
		greater->parent = node;  // This is done to make generating the encryption table easier
		
		if ( huffmanEncodingTreeNodeList.Size() == 0 )
		{
			// 3. Assign the one remaining node in the list to the root node.
			root = node;
			root->parent = 0;
			break;
		}
		
		// Put the new node back into the list at the correct spot to maintain the sort.  Linear search time
		InsertNodeIntoSortedList( node, &huffmanEncodingTreeNodeList );
	}
	
	bool tempPath[ 256 ]; // Maximum path length is 256
	unsigned short tempPathLength;
	HuffmanEncodingTreeNode *currentNode;
	RakNet::BitStream bitStream;
	
	// Generate the encryption table. From before, we have an array of pointers to all the leaves which contain pointers to their parents.
	// This can be done more efficiently but this isn't bad and it's way easier to program and debug
	
	for ( counter = 0; counter < 256; counter++ )
	{
		// Already done at the end of the loop and before it!
		tempPathLength = 0;
		
		// Set the current node at the leaf
		currentNode = leafList[ counter ];
		
		do
		{
			if ( currentNode->parent->left == currentNode )   // We're storing the paths in reverse order.since we are going from the leaf to the root
				tempPath[ tempPathLength++ ] = false;
			else
				tempPath[ tempPathLength++ ] = true;
				
			currentNode = currentNode->parent;
		}
		
		while ( currentNode != root );
		
		// Write to the bitstream in the reverse order that we stored the path, which gives us the correct order from the root to the leaf
		while ( tempPathLength-- > 0 )
		{
			if ( tempPath[ tempPathLength ] )   // Write 1's and 0's because writing a bool will write the BitStream TYPE_CHECKING validation bits if that is defined along with the actual data bit, which is not what we want
				bitStream.Write1();
			else
				bitStream.Write0();
		}
		
		// Read data from the bitstream, which is written to the encoding table in bits and bitlength. Note this function allocates the encodingTable[counter].encoding pointer
		encodingTable[ counter ].bitLength = ( unsigned char ) bitStream.CopyData( &encodingTable[ counter ].encoding );
		
		// Reset the bitstream for the next iteration
		bitStream.Reset();
//.........这里部分代码省略.........