private static void DecodeHeader(Stream input, Stream output, DecodingCodeTreeNode codeTree)
{
byte outputValue = 0;
byte inputValue;
// Loop until a byte with value 0xFF is encountered
while ((inputValue = NeutralEndian.Read1(input)) != 0xFF)
{
if ((inputValue & 0x80) != 0)
{
outputValue = (byte)(inputValue & 0xF);
inputValue = NeutralEndian.Read1(input);
}
codeTree.SetCode(
NeutralEndian.Read1(input),
inputValue & 0xF,
new NibbleRun(outputValue, (byte)(((inputValue & 0x70) >> 4) + 1)));
}
// Store a special nibble run for inline RLE sequences (code = 0b111111, length = 6)
// Length = 0xFF in the nibble run is just a marker value that will be handled specially in DecodeInternal
codeTree.SetCode(0x3F, 6, new NibbleRun(0, 0xFF));
}
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 CompressionException(Properties.Resources.InvalidCode);
}
}
}
outputBits.Flush(false);
}
finally
{
if (xorStream != null)
{
xorStream.Dispose();
}
}
}
