/// <summary>
/// Stores meta data (i.e. data needed to decompress and test the file) for the compressed <paramref name="filePart" />
/// .
/// </summary>
/// <param name="filePart">The compressed file which meta data should be stored.</param>
/// <param name="frequencyTable">The frequency table needed to restore the Huffman tree (for file decoding). </param>
/// <param name="uncompressedHashSum">The hashsum needed to test file correctness after unpacking.</param>
/// <param name="compressedHashSum">The hashsum needed to test compressed file correctness before unpacking.</param>
/// <param name="ratio">The compression ratio shown to the user.</param>
/// <param name="uncompressed">Size of the file before compression.</param>
/// <param name="compressed">Size of the compressed file.</param>
private void StoreMetaData(PackagePart filePart, FrequencyTable frequencyTable, byte[] uncompressedHashSum,
byte[] compressedHashSum, double ratio, long uncompressed, long compressed, string name)
{
/* collect metadate into a class */
var meta = new FileMetaData
{
frequencyTable = frequencyTable,
compressedHash = compressedHashSum,
uncompressedHash = uncompressedHashSum,
compressionRatio = ratio,
uncompressedSize = uncompressed,
compressedSize = compressed,
filename = name
};
/* create path (relating to the archive root) where the meta data will be stored */
var metaUri = PackUriHelper.CreatePartUri(new Uri(filePart.Uri + "META", UriKind.Relative));
/* create a package part in the path */
var metaPart = _archive.CreatePart(metaUri, "", CompressionOption.NotCompressed);
filePart.CreateRelationship(metaUri, TargetMode.Internal, ".\\META");
using (var metaStream = new BufferedStream(metaPart.GetStream(), BufferSize))
{
var formatter = new BinaryFormatter();
formatter.Serialize(metaStream, meta);
}
}
/// <summary>
/// Compresses the file stored in the <paramref name="path" /> and stores compressed file it the
/// <paramref name="filePart" />.
/// </summary>
/// <param name="path">The path to the file to be compressed.</param>
/// <param name="filePart">The archive part to store the compressed file in.</param>
/// <param name="frequencyTable">The frequency table to be saved to the archive.</param>
private void CompressFile(string path, PackagePart filePart, out FrequencyTable frequencyTable)
{
/* open the file */
var fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, BufferSize);
/* find frequencies of bytes in the file */
OnStateChange("counting up frequencies of bytes");
frequencyTable = new FrequencyTable(fileStream);
frequencyTable.SubscribeToUpdates(OnProgressChange);
frequencyTable.CountFrequencies();
/* rewind the position of the stream to use this stream once again */
fileStream.Position = 0;
/* build the Huffman tree based on the counted frequencies */
OnStateChange("building the Huffman tree");
var huffmanTree = new HuffmanTree(frequencyTable);
/* get the Huffman code from the tree */
OnStateChange("retrieving the Huffman code");
var encodingTable = new EncodingTable(huffmanTree);
/* get the file part's stream */
var filePartStream = new BufferedStream(filePart.GetStream(), BufferSize);
/* encode the file */
OnStateChange("compressing the file");
var encoder = new Encoder(fileStream, filePartStream, encodingTable);
encoder.SubscribeToUpdates(OnProgressChange);
encoder.Encode();
/* dispose unused streams */
fileStream.Close();
filePartStream.Close();
}
/// <summary>
/// Initializes a new instance of the decoder.
/// </summary>
/// <param name="frequencyTable">The frequency table to build the Huffman tree from.</param>
/// <param name="encoodedBytesCount">The number of bytes that should be decoded and written.</param>
public Decoder(Stream input, Stream output, FrequencyTable frequencyTable, long encoodedBytesCount)
{
InputStream = input;
OutputStream = output;
Tree = new HuffmanTree(frequencyTable);
BytesCount = encoodedBytesCount;
}
/// <summary>
/// Packs non-zero frequency bytes to Huffman tree leaves and joins it to corresponding bytes' frequencies.
/// </summary>
/// <param name="freq">The frequency table to get nodes from.</param>
/// <returns>Weighted nodes containing Huffman tree leaves and their weights.</returns>
private static WeightedNode[] PackNodes(FrequencyTable freq)
{
var weightedNodes = new List <WeightedNode>();
for (int @byte = byte.MinValue; @byte <= byte.MaxValue; @byte++)
{
/* for each byte in the frequency table */
if (freq[@byte] != 0)
{
/* if the byte occurs in the stream at least once */
weightedNodes.Add(new WeightedNode {
node = new Leaf(@byte), weight = freq[@byte]
});
}
}
return(weightedNodes.ToArray());
}
public static Node GenerateHuffmanTree(FrequencyTable frequencyTable, out int height)
{
//TODO enhance this code (assuming that both arrays have the same lenght)
/* check frequency table */
if (frequencyTable == null)
{
throw new ArgumentNullException(nameof(frequencyTable), "The provided frequency table is null.");
}
/* set initial height */
height = 0;
/* the array contaning leaves of a tree */
var leaves = PackNodes(frequencyTable);
Array.Sort(leaves);
if (leaves.Length == 1)
{
return(leaves[0].node);
height = 1;
}
if (leaves.Length == 0)
{
return(null);
}
/* the array containing internal nodes of a tree */
var
internalNodes =
new WeightedNode[leaves.Length -
1]; // (because Huffman tree is a full binary tree the array containg leaves-1 elements)
/* fill internailNodes with null values (null means node of infinite weight) */
FillWithNull(ref internalNodes);
/* the index of the current element of the leaves array */
var leavesIndex = 0;
/* the index of the current element of the internalNodes array */
var internalNodesIndex = 0;
var internalNodesEnd = 0;
/* current sum value */
long currentSum;
/* current (withing a loop iteration) min sum value */
long minSum;
/* special marker variable for determining the exact two elements of the min sum */
var status = "";
for (var i = 0; i <= internalNodes.Length - 1; i++)
/* while */
{
height += 1;
minSum = long.MaxValue;
if (leavesIndex + 1 < leaves.Length)
/* if two sequential elements (relating to leavesIndex) of leaves array exist */
{
/* check if their sum is less than the min sum (and set it as the new min sum if so) */
currentSum = leaves[leavesIndex].weight + leaves[leavesIndex + 1].weight;
if (currentSum < minSum)
{
minSum = currentSum;
status = "leaves + leaves";
}
}
if (leavesIndex < leaves.Length && internalNodes[internalNodesIndex] != null)
/* if current internal node's weight is not equal to infinity */
{
/* check if sum of current leaf and internal node is less than the min sum (and set it as the new min sum if so) */
currentSum = leaves[leavesIndex].weight + internalNodes[internalNodesIndex].weight;
if (currentSum < minSum)
{
minSum = currentSum;
status = "leaves + internalNodes";
}
}
if (internalNodes[internalNodesIndex] != null && internalNodesIndex + 1 < internalNodes.Length)
{
/* if two sequential elements (relating to internalNodesIndex) of internalNodes array exist */
if (internalNodes[internalNodesIndex + 1] != null)
{
/* check if sum of current leaf and internal node is less than the min sum (and set it as the new min sum if so) */
currentSum = internalNodes[internalNodesIndex].weight +
internalNodes[internalNodesIndex + 1].weight;
if (currentSum < minSum)
{
minSum = currentSum;
status = "internalNodes + internalNodes";
}
}
}
WeightedNode w1, w2;
switch (status)
{
case "leaves + leaves":
w1 = leaves[leavesIndex];
w2 = leaves[leavesIndex + 1];
internalNodes[internalNodesEnd++] = new WeightedNode
{
node = new InternalNode(w1.node, w2.node),
weight = w1.weight + w2.weight
};
leavesIndex += 2;
break;
case "leaves + internalNodes":
w1 = leaves[leavesIndex];
w2 = internalNodes[internalNodesIndex];
internalNodes[internalNodesEnd++] = new WeightedNode
{
node = new InternalNode(w1.node, w2.node),
weight = w1.weight + w2.weight
};
leavesIndex += 1;
internalNodesIndex += 1;
break;
case "internalNodes + internalNodes":
w1 = internalNodes[internalNodesIndex];
w2 = internalNodes[internalNodesIndex + 1];
internalNodes[internalNodesEnd++] = new WeightedNode
{
node = new InternalNode(w1.node, w2.node),
weight = w1.weight + w2.weight
};
internalNodesIndex += 2;
break;
default:
throw new NotImplementedException();
}
}
return(internalNodes[internalNodes.Length - 1].node);
}
