private static void traverseTree(TreeNode<int, byte> startNode, string codeword)
{
if (startNode.Left == null && startNode.Right == null)
{
frequencyTable.Codewords[startNode.Value] = codeword;
}
else
{
if (startNode.Left != null)
{
traverseTree(startNode.Left, codeword + "0");
}
if (startNode.Right != null)
{
traverseTree(startNode.Right, codeword + "1");
}
}
}
public static void DecodeStream(Stream inStream, Stream outStream)
{
int i = 0; // counter
byte streamLength = 0, readCharacters = 0;
// the root of Huffman Tree
TreeNode<int, byte> huffmanTreeRoot = new TreeNode<int, byte>(-1, 0);
TreeNode<int, byte> currentNode;
frequencyTable = new FrequencyTable();
readHuffmanTreeFromStream(inStream);
streamLength = (byte)inStream.ReadByte();
i = 0;
// construct A Huffman Tree
for (i = 0; i < frequencyTable.MaxTableSize; i++)
{
if (frequencyTable.Hits[i] != 0)
{
currentNode = huffmanTreeRoot;
foreach (char c in frequencyTable.Codewords[i])
{
if (c == '0')
{
if (currentNode.Left == null)
currentNode.Left = new TreeNode<int, byte>(-1, 0);
currentNode = currentNode.Left;
}
else if (c == '1')
{
if (currentNode.Right == null)
currentNode.Right = new TreeNode<int, byte>(-1, 0);
currentNode = currentNode.Right;
}
}
currentNode.Key = 1; // this node contains a character (is a leaf)
currentNode.Value = (byte)i;
}
}
// Tree is ready, start decoding
string buffer = "", bits = "";
//string pooledBuffer = "";
int nextByte = 0, nextNextByte;
i = 0;
nextNextByte = inStream.ReadByte();
while (nextByte != -1)
{
nextByte = nextNextByte;
nextNextByte = inStream.ReadByte();
bits = decodeByteToBitString((byte)nextByte);
if (bits.Length < 8)
bits += new string('0', 8 - bits.Length);
buffer += bits;
//pooledBuffer += bits;
currentNode = huffmanTreeRoot; // start from Tree root
for (i = 0; i < buffer.Length; i++)
{
if (nextNextByte == -1) // end of stream
{
if (readCharacters == streamLength)
break;
}
if (buffer[i] == '0')
currentNode = currentNode.Left;
else
currentNode = currentNode.Right;
if (currentNode.Key == 1) // character found
{
++readCharacters;
outStream.WriteByte(currentNode.Value);
buffer = buffer.Substring(i + 1);
i = -1;
currentNode = huffmanTreeRoot;
}
}
//nextByte = inStream.ReadByte();
}
}
private static int compareTreeNodes(TreeNode<int, byte> node1, TreeNode<int, byte> node2)
{
if (node1 == null || node2 == null)
return 0;
if (node1.Key == node2.Key)
return 0;
else if (node1.Key > node2.Key)
return 1;
else
return -1;
}
public static void EncodeStream(Stream inStream, Stream outStream)
{
int i = 0; // counter
int newFreq;
// the list of all Huffman Tree nodes
List<TreeNode<int, byte>> huffmanTree = new List<TreeNode<int, byte>>();
// the root of Huffman Tree
TreeNode<int, byte> huffmanTreeRoot = new TreeNode<int, byte>(0, 0);
frequencyTable = new FrequencyTable();
/*frequencyTable = new FrequencyEntry[256 ];
for (i = 0; i < frequencyTable.Length; ++i)
frequencyTable[i] = new FrequencyEntry();*/
calculateFrequency(inStream);
i = 0;
// construct a forest
for (i = 0; i < frequencyTable.MaxTableSize; i++)
{
if (frequencyTable.Hits[i] != 0)
// add a new node to Huffman Tree, where character hits is the key
// and the character itself is the value
huffmanTree.Add(new TreeNode<int, byte>(frequencyTable.Hits[i], (byte)i));
}
// link the nodes
while (huffmanTree.Count > 1)
{
huffmanTree.Sort(compareTreeNodes);
newFreq = huffmanTree[0].Key + huffmanTree[1].Key;
TreeNode<int, byte> node = new TreeNode<int, byte>(newFreq, 0);
node.Left = huffmanTree[0];
node.Right = huffmanTree[1];
node.Left.Parent = node;
node.Right.Parent = node;
huffmanTree.RemoveAt(0);
huffmanTree.RemoveAt(0);
huffmanTree.Add(node);
huffmanTreeRoot = node;
}
//calculate codewords
traverseTree(huffmanTreeRoot, "");
//wrtie table
writeHuffmanTreeToStream(outStream);
//
outStream.WriteByte((byte)(inStream.Length % 256));
//wrtie encoded stream
//string buffer = "", bits = "";
//string pooledBuffer = "";
BitBuffer bitBuffer = new BitBuffer(1, outStream);
int nextChar = 0;
inStream.Seek(0, SeekOrigin.Begin);
nextChar = inStream.ReadByte();
while (nextChar != -1)
{
bitBuffer.AddToBuffer(frequencyTable.Codewords[nextChar]);
//pooledBuffer += frequencyTable.Codewords[nextChar];
/*if (buffer.Length >= 8)
{
bits = buffer.Substring(0, 8);
buffer = buffer.Substring(8);
outStream.WriteByte(encodeBitString(bits));
}*/
nextChar = inStream.ReadByte();
}
bitBuffer.Flush();
//if (buffer.Length > 0)
// outStream.WriteByte(encodeBitString(buffer));
}