public HuffNode(byte symbol)
{
IsBranch = false;
Symbol = symbol;
Weight = 1;
Left = Right = null;
}
public HuffNode(int weight, HuffNode left, HuffNode right)
{
IsBranch = true;
Symbol = 0;
Weight = weight;
Left = left;
Right = right;
}
/*
* Pack
* Encode 1 or more byte streams into a Huffman archive
*
* List<byte[]> files = List of byte streams (files)
*/
public static byte[] Pack(List <byte[]> files)
{
int numFiles = files.Count;
// scan files to get symbols and their respective weights
List <HuffNode> nodes = new List <HuffNode>();
for (int i = 0; i < files.Count; i++)
{
for (int j = 0; j < files[i].Length; j++)
{
if (nodes.Count == 0)
{
nodes.Add(new HuffNode(files[i][j]));
}
else
{
bool nodeFound = false;
for (int n = 0; n < nodes.Count; n++)
{
if (nodes[n].Symbol == files[i][j])
{
nodes[n].Weight++;
nodeFound = true;
break;
}
}
if (!nodeFound)
{
nodes.Add(new HuffNode(files[i][j]));
}
}
}
}
// sort the Nodes into a priority queue (in ascending weight order)
nodes.Sort((x, y) => x.Weight.CompareTo(y.Weight));
// build tree
while (nodes.Count > 1)
{
HuffNode left = nodes[0];
HuffNode right = nodes[1];
int weight = nodes[0].Weight + nodes[1].Weight;
nodes.RemoveRange(0, 2);
HuffNode branch = new HuffNode(weight, left, right);
int n = 0;
while (n < nodes.Count)
{
if (branch.Weight <= nodes[n].Weight)
{
break;
}
n++;
}
nodes.Insert(n, branch);
}
// traverse tree and write it, also saving the hash codes for each symbol
List <byte> chars = new List <byte>();
List <bool> tree = new List <bool>();
List <HuffCode> huffCodes = new List <HuffCode>();
nodes[0].Traverse(chars, tree, huffCodes, new List <bool>());
// initialise byte stream that will eventually be returned
List <byte> stream = new List <byte>();
// write # files
stream.Add(0);
stream.Add((byte)numFiles);
// write # chars
stream.Add((byte)(chars.Count >> 8));
stream.Add((byte)chars.Count);
// write file headers & prepare data
List <bool> data = new List <bool>();
foreach (byte[] file in files)
{
// write byte offset
ushort offset = (ushort)(2 + 2 + (6 * numFiles) + chars.Count + Math.Ceiling(((decimal)tree.Count) / 8) + (data.Count / 8));
byte msb = (byte)(offset >> 8);
byte lsb = (byte)(offset & 0x00FF);
stream.Add(msb);
stream.Add(lsb);
// write bit offset
lsb = (byte)(data.Count % 8);
stream.Add(0);
stream.Add(lsb);
// write unpacked data length
ushort len = (ushort)file.Length;
msb = (byte)(len >> 8);
lsb = (byte)(len & 0x00FF);
stream.Add(msb);
stream.Add(lsb);
// process each byte in the file and write the packed hash
foreach (byte symbol in file)
{
foreach (HuffCode huffCode in huffCodes)
{
if (symbol == huffCode.Symbol)
{
data.AddRange(huffCode.HashString);
break;
}
}
}
}
// write chars
stream.AddRange(chars);
// write tree
stream.AddRange(bitsToBytes(tree));
// write data
stream.AddRange(bitsToBytes(data));
return(stream.ToArray());
}
