public void Compress(Stream source, Stream target)
{
using (var sourceFile = new BitFile(source, BitFileMode.Read))
using (var targetFile = new BitFile(target, BitFileMode.Write))
{
Compress(sourceFile, targetFile);
}
}
public void Decompress(string sourcePath, string targetPath)
{
using (var sourceFile = new BitFile(sourcePath, BitFileMode.Read))
using (var targetFile = new BitFile(targetPath, BitFileMode.Write))
{
Decompress(sourceFile, targetFile);
}
}
public ArithmeticDecoder(BitFile sourceFile)
{
_sourceFile = sourceFile;
for (int i = 0; i < 32; i++) // initialize with first 4 bytes
{
previousBytes = (previousBytes << 1) | sourceFile.Read();
}
}
private void EncodeHeader(BitFile targetFile, long size)
{
string header = $"PAQ1\r\n{size}\0";
var headerBytes = Encoding.ASCII.GetBytes(header);
foreach (var headerByte in headerBytes)
{
targetFile.Write(headerByte);
}
}
private void Decompress(BitFile sourceFile, BitFile targetFile)
{
long originalSize = DecodeHeader(sourceFile);
var predictor = new Predictor();
var decoder = new ArithmeticDecoder(sourceFile);
while (targetFile.Length < originalSize)
{
double p0 = predictor.Predict();
var bit = decoder.Decode(p0);
targetFile.Write(bit);
predictor.Update((int)bit);
}
}
private void Compress(BitFile sourceFile, BitFile targetFile)
{
EncodeHeader(targetFile, sourceFile.Length);
var predictor = new Predictor();
var encoder = new ArithmeticEncoder(targetFile);
while (!sourceFile.IsEof)
{
var bit = sourceFile.Read();
double p0 = predictor.Predict();
// todo: remove casting
encoder.Encode((int)bit, p0);
predictor.Update((int)bit);
}
encoder.EncodeRemainingBits();
}
private long DecodeHeader(BitFile sourceFile)
{
byte endOfHeader = Encoding.ASCII.GetBytes("\0")[0];
var headerBytes = new List <byte>();
byte headerByte;
do
{
headerByte = sourceFile.ReadByte();
headerBytes.Add(headerByte);
} while (headerByte != endOfHeader);
string header = Encoding.ASCII.GetString(headerBytes.ToArray());
if (header.Substring(0, 6) != "PAQ1\r\n")
{
throw new NotSupportedException("Bad PAQ1 header format.");
}
var size = header.Substring(6, header.Length - 7);
return(long.Parse(size));
}
public ArithmeticEncoder(BitFile targetFile)
{
_targetFile = targetFile;
}