// encodes `text` and writes to `filename`, returns compression info
public static CompressionInfo Encode(string text, string filename)
{
BinaryWriter writer;
try
{
writer = new BinaryWriter(File.Open(filename, FileMode.Create));
}
catch
{
throw;
}
if (text.Length == 0)
{
// create an empty file
writer.Close();
return(new CompressionInfo(0, 0, 0, 0));
}
// 0. generate the tree and the code table
HuffmanTree tree = HuffmanTree.GenerateHuffmanTree(text);
HuffmanCodeTable codeTable = new HuffmanCodeTable(tree);
// 1. encode
// 1.1. encode the tree
ushort[] treeBuffer = new ushort[codeTable.NumberOfCodes * 2];
int treeBitPosition = 0;
EncodeTree(tree, treeBuffer, ref treeBitPosition);
int treeLengthInBytes = treeBitPosition / 8;
byte bitsOfLastByteOfTree = (byte)(treeBitPosition % 8);
if (bitsOfLastByteOfTree == 0)
{
bitsOfLastByteOfTree = 8;
}
else
{
treeLengthInBytes++;
}
// 1.2. encode the text
char[] textCharArray = text.ToCharArray();
ushort[] encodedTextBuffer = new ushort[textCharArray.Length];
long encodedTextBitPosition = 0;
for (int i = 0; i < textCharArray.Length; i++)
{
AppendCode(encodedTextBuffer, codeTable.GetHuffmanCode(textCharArray[i]), ref encodedTextBitPosition);
}
textCharArray = null;
int encodedTextLengthInBytes = (int)(encodedTextBitPosition / 8);
byte bitsOfLastByteOfEncodedText = (byte)(encodedTextBitPosition % 8);
if (bitsOfLastByteOfEncodedText == 0)
{
bitsOfLastByteOfEncodedText = 8;
}
else
{
encodedTextLengthInBytes++;
}
// 2. write
try
{
// 2.1. write the metadata
// first 6 bits of the file is for FileFormatVersion,
// next 18 bits for treeLengthInBytes,
// next 4 bits for bitsOfLastByteOfTree,
// next 4 bits for bitsOfLastByteOfEncodedText
// (4 bytes for metadata in total)
writer.Write((byte)((FileFormatVersion << 2) | (treeLengthInBytes >> 16)));
writer.Write((byte)(treeLengthInBytes >> 8));
writer.Write((byte)(treeLengthInBytes));
writer.Write((byte)((bitsOfLastByteOfTree << 4) | bitsOfLastByteOfEncodedText));
// 2.2. write the encoded tree
WriteBuffer(writer, treeBuffer, treeBitPosition);
// 2.3. write the encoded text
WriteBuffer(writer, encodedTextBuffer, encodedTextBitPosition);
}
catch
{
throw;
}
finally
{
writer.Close();
}
return(new CompressionInfo(text.Length, 4, treeLengthInBytes, encodedTextLengthInBytes));
}
