public void DecodeFlag()
{
var bytes = BitConverter.GetBytes(0b10011_10); // val = 0x33
var bs = new BitReadStream(bytes);
var(rlen, rmap) = TransformTable.DecodeFlag(bs);
Assert.AreEqual <int>(5, rlen);
var rval = (int)bs.Read(rlen);
Assert.AreEqual <byte>(0x33, rmap[rval]);
}
public byte[] Decode(byte[] flag, byte[] residual)
{
var flagIn = new BitReadStream(flag);
var resOut = new ByteBuffer();
// Actual residual length
int resLength = residual.Length;
try {
while (!flagIn.IsEOF)
{
// Parse residual header
int kset = residual[0] >> 3;
int fbits = residual[0] & 7;
// Initialize residual reader and discard header
var resIn = new BitReadStream(residual, resLength * 8 - fbits);
resIn.Read(8);
// Perform inverse MV2 substitutions
for (int i = 0; !resIn.IsEOF; i++)
{
var(rlen, rmap) = TransformTable.DecodeFlag(flagIn);
byte val = rmap[resIn.Read(rlen)];
// Unscramble byte values after MV2 decoding
val = key.XorByte(key.Decode(val, kset), i);
resOut.Write(val);
}
// Skip flag padding
flagIn.FinishByte();
// Forward the residual to the next round
residual = resOut.GetBytesInternal();
resLength = resOut.Position;
resOut.Reset();
}
} catch (ArgumentException ex) {
throw new DecoderException(ex);
} catch (IndexOutOfRangeException ex) {
throw new DecoderException(ex);
}
// Trim final output
var output = new byte[resLength];
Array.Copy(residual, output, resLength);
return(output);
}