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|
using System;
using System.Collections.Generic;
using System.IO;
namespace MagicHuffman
{
/// <summary>
/// Represents an Huffman tree node.
/// It will always have two child nodes or zero.
/// If it has child nodes, then it doesn't have a value, otherwise it does.
/// </summary>
public class HuffmanNode : IComparable
{
private HuffmanNode[] nodes;
private byte data;
private int weight;
/// <summary>
/// Creates a valued node.
/// </summary>
/// <param name="data">Value</param>
/// <param name="weight">Number of occurences of the value in the input document</param>
public HuffmanNode(byte data, int weight)
{
nodes = null;
Data = data;
Weight = weight;
}
/// <summary>
/// Create a parent node.
/// </summary>
/// <param name="left">Left node</param>
/// <param name="right">Right node</param>
public HuffmanNode(HuffmanNode left, HuffmanNode right)
{
nodes = new HuffmanNode[2];
Left = left;
Right = right;
}
/// <summary>
/// Node's data
/// </summary>
public byte Data
{
get
{
if (nodes != null)
{
throw new InvalidOperationException("This node doesn't have a value as it has children.");
}
return data;
}
set
{
if (nodes != null)
{
throw new InvalidOperationException("This node can't have a value as it has children.");
}
data = value;
}
}
/// <summary>
/// Node's weight (weight of the data, or sum of the children nodes' weight).
/// </summary>
public int Weight
{
get
{
if (nodes != null)
{
return Left.Weight + Right.Weight;
}
else
{
return weight;
}
}
set
{
if (nodes != null)
{
throw new InvalidOperationException("This node weight can't be set as it has children.");
}
weight = value;
}
}
/// <summary>
/// Left child node
/// </summary>
public HuffmanNode Left
{
get
{
if (nodes == null)
{
return null;
}
else
{
return nodes[0];
}
}
set
{
if (nodes == null)
{
throw new InvalidOperationException("This node can't have children as it is valued.");
}
nodes[0] = value;
}
}
/// <summary>
/// Right child node
/// </summary>
public HuffmanNode Right
{
get
{
if (nodes == null)
{
return null;
}
else
{
return nodes[1];
}
}
set
{
if (nodes == null)
{
throw new InvalidOperationException("This node can't have children as it is valued.");
}
nodes[1] = value;
}
}
/// <summary>
/// Compares the weight of the node
/// </summary>
/// <param name="obj">Another HuffmanNode instance</param>
/// <returns>Comparision of the weight of the two nodes</returns>
/// <exception cref="ArgumentException">obj must be a HuffmanNode</exception>
public int CompareTo(object obj)
{
if (obj is HuffmanNode)
{
return this.Weight.CompareTo((obj as HuffmanNode).Weight);
}
throw new ArgumentException("Object is not a HuffmanNode");
}
/// <summary>
/// Serialize (for debug purpose only) the node
/// </summary>
/// <param name="prefix">Prefix to add (from the parent nodes)</param>
/// <returns>String representing the serialized node</returns>
public string ToString(string prefix)
{
if (nodes == null)
{
return string.Format("{0}:{1}\r\n", (char)Data, prefix);
}
else
{
return string.Format("{0}{1}", Left.ToString(prefix + "1"), Right.ToString(prefix + "0"));
}
}
public void StoreNode(BitWriter writer)
{
if (nodes == null)
{
writer.WriteBit(1);
writer.WriteByte(Data);
}
else
{
writer.WriteBit(0);
Left.StoreNode(writer);
Right.StoreNode(writer);
}
}
public static HuffmanNode ReadNode(BitReader reader)
{
if (reader.ReadBit() == 1)
{
return new HuffmanNode(reader.ReadByte(), 0);
}
else
{
HuffmanNode left = ReadNode(reader);
HuffmanNode right = ReadNode(reader);
return new HuffmanNode(left, right);
}
}
}
public class BitWriter
{
private int bitPosition;
private Stream output;
private byte currentByte;
public BitWriter(Stream s)
{
output = s;
bitPosition = 0;
currentByte = 0;
}
public void WriteBit(byte bit)
{
currentByte |= (byte)(bit << 7 - bitPosition);
bitPosition++;
if (bitPosition == 8)
{
output.WriteByte(currentByte);
currentByte = 0;
bitPosition = 0;
}
}
public void WriteBits(uint bits, byte length)
{
// On doit pouvoir optimiser ça
for (byte i = 0; i < length; ++i)
{
WriteBit((byte)((bits >> 31 - i) & 0x1));
}
}
public void WriteByte(byte value)
{
WriteBits(((uint)value << 24), 8);
}
public void WriteHuffmanCode(HuffmanCode code)
{
WriteBits(code.Bits, code.Length);
}
public void Flush()
{
if (bitPosition > 0)
{
output.WriteByte(currentByte);
}
output.Flush();
}
}
public class BitReader
{
private byte bitPosition;
private Stream input;
private byte currentByte;
public BitReader(Stream s)
{
input = s;
input.Seek(0, SeekOrigin.Begin);
bitPosition = 0;
currentByte = (byte)input.ReadByte();
}
public byte ReadBit()
{
if (bitPosition == 8)
{
currentByte = (byte)input.ReadByte();
bitPosition = 0;
}
return (byte)((currentByte >> 7 - bitPosition++) & 0x1);
}
public byte ReadByte()
{
byte value = 0;
for (byte i = 0; i < 8; ++i)
{
value |= (byte)(ReadBit() << 7 - i);
}
return value;
}
public uint ReadBits(byte length)
{
uint res = 0;
// On doit pouvoir optimiser ça
for (byte i = 0; i < length; ++i)
{
res |= (uint)ReadBit() << (31 - i);
}
return res;
}
}
/// <summary>
/// Represents a "huffman code" (ie. 01101) and its length in order to make difference between 001 and 1.
/// </summary>
public struct HuffmanCode
{
/// <summary>
/// Code
/// </summary>
public uint Bits;
/// <summary>
/// Length of the code
/// </summary>
public byte Length;
}
/// <summary>
/// Use this class to compress and decompress a document using Huffman encoding
/// </summary>
public class Huffman
{
/// <summary>
/// Buffer size to be read/write from the streams. Can be freely tuned.
/// </summary>
private const int BUFFER_SIZE = 4096; // 4 Ko
private const int LAST_BIT_POS = BUFFER_SIZE << 3;
/// <summary>
/// Top of the Huffman tree (used to create the dictionary and to decode)
/// </summary>
private HuffmanNode root = null;
/// <summary>
/// Dictionary used to encode.
/// A SortedDictionary<T> may be used here, but I guess a simple array (with holes) is faster.
/// </summary>
private HuffmanCode[] dictionary = new HuffmanCode[256];
/// <summary>
/// Number of bytes in the uncompressed document
/// </summary>
private uint DocumentLength = 0;
/// <summary>
/// Instanciate a new empty huffman tree. It can be used only for decompression.
/// </summary>
public Huffman()
{
}
/// <summary>
/// Instanciate a new Huffman tree from a source document.
/// </summary>
/// <param name="s">Source document</param>
public Huffman(Stream s)
{
s.Seek(0, SeekOrigin.Begin);
// Create a temporary dictionary to enumerate any byte value and compute its weight
List<HuffmanNode> bytes = new List<HuffmanNode>(256);
for (int i = 0; i < 256; i++)
{
bytes.Add(new HuffmanNode((byte)i, 0));
}
// Document will be read by blocks
byte[] buffer = new byte[BUFFER_SIZE];
int read = 0;
// Read all the document to enumarate each byte weight
while ((read = s.Read(buffer, 0, BUFFER_SIZE)) > 0)
{
DocumentLength += (uint)read;
for (int i = 0; i < read; ++i)
{
// Increment byte weight
bytes[buffer[i]].Weight++;
}
}
// Remove any unused byte
for (int i = 255; i >= 0; --i)
{
if (bytes[i].Weight == 0)
{
bytes.RemoveAt(i);
}
}
// Construct the Huffman tree
while (bytes.Count > 1)
{
// Sort nodes from lowest weight to highest
bytes.Sort();
// Merge the two lowest weighted nodes togethers
HuffmanNode node = new HuffmanNode(bytes[0], bytes[1]);
bytes.RemoveAt(1);
bytes[0] = node;
}
// Root node of the tree is the lastest remaning node in the list
root = bytes[0];
// Destroy the List<> the is not used anymore
bytes = null;
// Build the dictionary used to encode (compress)
BuildDictionary(root, 0, 0);
}
/// <summary>
/// Builds a dictionary used to compress a document using the Huffman tree
/// </summary>
/// <param name="node">Parent node</param>
/// <param name="code">Prefix code from the parent node</param>
/// <param name="depth">Code length (depth of the node in the tree)</param>
private void BuildDictionary(HuffmanNode node, uint code, byte depth)
{
if (node.Left != null)
{
// The node has children : build dictionary from both children
++depth;
BuildDictionary(node.Left, (code << 1) | 0x1, depth);
BuildDictionary(node.Right, (code << 1), depth);
}
else
{
// The node has no child : build dictionary from both children
dictionary[node.Data] = new HuffmanCode() { Bits = code << (32 - depth), Length = depth };
}
}
/// <summary>
/// Compresses the input stream to the output stream using huffman encoding
/// </summary>
/// <param name="input">Source document</param>
/// <param name="output">Compressed document</param>
public void Compress(Stream input, BitWriter output)
{
// Step 1 : Store document length
output.WriteBits(DocumentLength, 32);
// Step 2 : Store dictionary
root.StoreNode(output);
byte[] inputbuffer = new byte[BUFFER_SIZE];
int read = 0;
input.Seek(0, SeekOrigin.Begin);
while ((read = input.Read(inputbuffer, 0, BUFFER_SIZE)) > 0)
{
for (int i = 0; i < read; ++i)
{
output.WriteHuffmanCode(dictionary[inputbuffer[i]]);
}
}
output.Flush();
}
/// <summary>
/// Uncompresses input stream to output stream using huffman encoding
/// </summary>
/// <param name="input">Compressed document</param>
/// <param name="output">Original document</param>
public void DeCompress(BitReader input, Stream output)
{
// Step 1 : Load document length
DocumentLength = input.ReadBits(32);
// Step 2 : Load dictionary
root = HuffmanNode.ReadNode(input);
//byte[] inputbuffer = new byte[BUFFER_SIZE + 4];
byte[] outputbuffer = new byte[BUFFER_SIZE];
//int bitPosition = 0;
int bytePosition = 0;
int totalLength = 0;
//input.Seek(0, SeekOrigin.Begin);
//read = input.Read(inputbuffer, 0, BUFFER_SIZE + 4);
while (totalLength < DocumentLength)
{
outputbuffer[bytePosition++] = GetByteFromBits(input);
totalLength++;
if (bytePosition == BUFFER_SIZE)
{
output.Write(outputbuffer, 0, BUFFER_SIZE);
bytePosition = 0;
}
}
if (bytePosition > 0)
{
output.Write(outputbuffer, 0, bytePosition);
}
}
/// <summary>
/// Gets a byte from bits using the instance's huffman dictionary
/// </summary>
/// <param name="reader">BitReader where to read bits from</param>
/// <returns>Decoded byte from the dictionary</returns>
public byte GetByteFromBits(BitReader reader)
{
HuffmanNode currentNode = root;
while (currentNode.Left != null)
{
if (reader.ReadBit() == 1)
{
currentNode = currentNode.Left;
}
else
{
currentNode = currentNode.Right;
}
}
return currentNode.Data;
}
/// <summary>
/// Serialize (for debug only) the huffman tree of the instance
/// </summary>
/// <returns></returns>
public override string ToString()
{
return root.ToString(string.Empty);
}
}
} |
