private void DecompressStream()
{
int codedLiteral; // true if literals are coded
int dictSize; // log2(dictionary size) - 6
int decodedSymbol; // decoded symbol, extra bits for distance
int copyLength; // length for copy
int copyDist; // distance for copy
int copyCount; // copy counter
int fromIndex;
// read header (start of compressed stream)
codedLiteral = GetBits(8);
if (codedLiteral > 1)
{
throw new BlastException(BlastException.LiteralFlagMessage);
}
dictSize = GetBits(8);
if (dictSize < 4 || dictSize > 6)
{
throw new BlastException(BlastException.DictionarySizeMessage);
}
// decode the compressed stream
try
{
// decode literals and length/distance pairs
do
{
if (GetBits(1) > 0)
{ // 0 == literal, 1 == length+distance
// decode length
decodedSymbol = Decode(HuffmanTable.LENGTH_CODE);
copyLength = LENGTH_CODE_BASE[decodedSymbol] + GetBits(LENGTH_CODE_EXTRA[decodedSymbol]);
if (copyLength == END_OF_STREAM) // sentinel value
{
// no more for this stream,
// stop and flush
break;
}
// decode distance
decodedSymbol = copyLength == 2 ? 2 : dictSize;
copyDist = Decode(HuffmanTable.DISTANCE_CODE) << decodedSymbol;
copyDist += GetBits(decodedSymbol);
copyDist++;
// malformed input - you can't go back that far
if (copyDist > this._outputBufferPos)
{
throw new BlastException(BlastException.DistanceMessage);
}
// Copy copyLength bytes from copyDist bytes back.
// If copyLength is greater than copyDist, repeatedly
// copy copyDist bytes up to a count of copyLength.
do
{
fromIndex = this._outputBufferPos - copyDist;
copyCount = copyDist;
if (copyCount > copyLength)
{
copyCount = copyLength;
}
CopyBufferSection(fromIndex, copyCount);
copyLength -= copyCount;
} while (copyLength != 0);
}
else
{
// get literal and write it
decodedSymbol = codedLiteral != 0 ? Decode(HuffmanTable.LITERAL_CODE) : GetBits(8);
WriteBuffer((byte)decodedSymbol);
}
} while (true);
}
finally
{
// write remaining bytes
FlushOutputBuffer();
FlushBits();
}
}
