private static Stream XORStream(Stream s)
{
byte compr_incremental_xor = 0x57;
var decompressedStream = new MemoryStream();
Reader reader = new Reader(s, Endian.Little); // No using, because we don't want to close the stream
byte bytes_in_window = reader.ReadByte();
bytes_in_window ^= 0x53;
decompressedStream.WriteByte(bytes_in_window);
uint decompressedSize = reader.ReadUInt32();
decompressedSize ^= 0x54555657;
decompressedStream.Write(BitConverter.GetBytes(decompressedSize), 0, 4);
while (s.Position < s.Length)
{
byte b = reader.ReadByte();
byte xor = 0;
// Bit reverse
for (int i = 0; i < 8; i++)
{
xor = (byte)BitHelpers.SetBits(xor, BitHelpers.ExtractBits(compr_incremental_xor, 1, i), 1, 7 - i);
}
b = (byte)(b ^ (xor ^ 0xB9));
if (compr_incremental_xor == 0xFF)
{
compr_incremental_xor = 0x0;
}
else
{
compr_incremental_xor++;
}
decompressedStream.WriteByte(b);
}
decompressedStream.Position = 0;
return(decompressedStream);
}
/// <summary>
/// Encodes the raw data
/// </summary>
/// <param name="inputStream">The raw data stream</param>
/// <param name="outputStream">The output stream</param>
/// <returns>The encrypted data</returns>
public void Encode(Stream inputStream, Stream outputStream)
{
Reader reader = new Reader(inputStream, Endian.Little);
using (Stream temp = new MemoryStream())
{
using (Writer writer = new Writer(temp, Endian.Little))
{
byte[] compr_big_window = new byte[256 * 8];
for (int i = 0; i < 256; i++)
{
for (int j = 0; j < 8; j++)
{
compr_big_window[i * 8 + j] = (byte)i;
}
}
byte[] compr_window = new byte[8];
for (int j = 0; j < 8; j++)
{
compr_window[j] = 0;
}
writer.Write((byte)0); // checksum
writer.Write((uint)0); // size
uint startPos = (uint)reader.BaseStream.Position;
writer.BeginCalculateChecksum(new Checksum8Calculator());
bool isFinished = false;
while (!isFinished)
{
uint num_bytesToCompress = 0;
for (int i = 0; i < 8; i++)
{
if (reader.BaseStream.Position >= reader.BaseStream.Length)
{
break;
}
num_bytesToCompress++;
byte b = reader.ReadByte();
compr_window[i] = b;
}
if (num_bytesToCompress > 0)
{
int maxOccurrencesInBigWindow = -1;
int bestBigWindowI = 0;
for (int i = 0; i < 256; i++)
{
int occurrencesInBigWindow = 0;
for (int j = 0; j < num_bytesToCompress; j++)
{
if (compr_big_window[i * 8 + j] == compr_window[j])
{
occurrencesInBigWindow++;
}
}
if (occurrencesInBigWindow > maxOccurrencesInBigWindow)
{
maxOccurrencesInBigWindow = occurrencesInBigWindow;
bestBigWindowI = i;
if (occurrencesInBigWindow == num_bytesToCompress)
{
break;
}
}
}
writer.Write((byte)bestBigWindowI);
byte windowUpdateBitArray = 0;
for (int i = 0; i < Math.Min(8, num_bytesToCompress); i++)
{
if (compr_big_window[bestBigWindowI * 8 + i] != compr_window[i])
{
windowUpdateBitArray = (byte)BitHelpers.SetBits(windowUpdateBitArray, 1, 1, i);
}
}
writer.Write(windowUpdateBitArray);
for (int i = 0; i < 8; i++)
{
if (windowUpdateBitArray % 2 == 1)
{
writer.Write((byte)compr_window[i]);
}
windowUpdateBitArray /= 2;
}
if (num_bytesToCompress >= 8)
{
for (int i = 0; i < 8; i++)
{
compr_big_window[bestBigWindowI * 8 + i] = compr_window[i];
}
}
else
{
writer.Write((byte)num_bytesToCompress);
isFinished = true;
}
}
else
{
isFinished = true;
}
}
byte checksum = writer.EndCalculateChecksum <byte>();
uint decompressedSize = (uint)reader.BaseStream.Position - startPos;
writer.BaseStream.Position = 0;
writer.Write((byte)checksum);
writer.Write((uint)decompressedSize);
writer.BaseStream.Position = 0;
using (Stream xor = XORStream(writer.BaseStream))
xor.CopyTo(outputStream);
}
}
}
