private static void DecodeNibbleRun(UInt8_E_L_InputBitStream inputBits, UInt8_E_L_OutputBitStream outputBits, byte count, byte nibble, ref int bitsWritten)
{
bitsWritten += count * 4;
// Write single nibble, if needed
if ((count & 1) != 0)
{
outputBits.Write(nibble, 4);
}
// Write pairs of nibbles
count >>= 1;
nibble |= (byte)(nibble << 4);
while (count-- != 0)
{
outputBits.Write(nibble, 8);
}
}
private static void DecodeInternal(Stream input, Stream output, DecodingCodeTreeNode codeTree, ushort numberOfTiles, bool xorOutput)
{
UInt8_E_L_InputBitStream inputBits = new UInt8_E_L_InputBitStream(input);
UInt8_E_L_OutputBitStream outputBits;
XorStream xorStream = null;
try
{
if (xorOutput)
{
xorStream = new XorStream(output);
outputBits = new UInt8_E_L_OutputBitStream(xorStream);
}
else
{
outputBits = new UInt8_E_L_OutputBitStream(output);
}
// The output is: number of tiles * 0x20 (1 << 5) bytes per tile * 8 (1 << 3) bits per byte
int outputSize = numberOfTiles << 8; // in bits
int bitsWritten = 0;
DecodingCodeTreeNode currentNode = codeTree;
while (bitsWritten < outputSize)
{
NibbleRun nibbleRun = currentNode.NibbleRun;
if (nibbleRun.Count == 0xFF)
{
// Bit pattern 0b111111; inline RLE.
// First 3 bits are repetition count, followed by the inlined nibble.
byte count = (byte)(inputBits.Read(3) + 1);
byte nibble = inputBits.Read(4);
DecodeNibbleRun(inputBits, outputBits, count, nibble, ref bitsWritten);
currentNode = codeTree;
}
else if (nibbleRun.Count != 0)
{
// Output the encoded nibble run
DecodeNibbleRun(inputBits, outputBits, nibbleRun.Count, nibbleRun.Nibble, ref bitsWritten);
currentNode = codeTree;
}
else
{
// Read the next bit and go down one level in the tree
currentNode = currentNode[inputBits.Get()];
if (currentNode == null)
{
throw new Exception("InvalidCode");
}
}
}
outputBits.Flush(false);
}
finally
{
if (xorStream != null)
{
xorStream.Dispose();
}
}
}