private static LinkedNode Decode(BitStream input, LinkedNode head)
{
LinkedNode node = head;
while (node.Child0 != null)
{
int num = input.ReadBits(1);
if (num == -1)
{
throw new Exception("Unexpected end of file");
}
node = (num == 0) ? node.Child0 : node.Child1;
}
return(node);
}
// Return values:
// 0x000 - 0x0FF : One byte from compressed file.
// 0x100 - 0x305 : Copy previous block (0x100 = 1 byte)
// -1 : EOF
private int DecodeLit()
{
switch (_bitstream.ReadBits(1))
{
case -1:
return(-1);
case 1:
// The next bits are position in buffers
int pos = sPosition2[_bitstream.PeekByte()];
// Skip the bits we just used
if (_bitstream.ReadBits(sLenBits[pos]) == -1)
{
return(-1);
}
int nbits = sExLenBits[pos];
if (nbits != 0)
{
// TODO: Verify this conversion
int val2 = _bitstream.ReadBits(nbits);
if (val2 == -1 && (pos + val2 != 0x10e))
{
return(-1);
}
pos = sLenBase[pos] + val2;
}
return(pos + 0x100); // Return number of bytes to repeat
case 0:
if (_compressionType == CompressionType.Binary)
{
return(_bitstream.ReadBits(8));
}
// TODO: Text mode
throw new NotImplementedException("Text mode is not yet implemented");
default:
return(0);
}
}
public static MemoryStream Decompress(Stream data)
{
int comptype = data.ReadByte();
if (comptype == 0)
{
throw new NotImplementedException("Compression type 0 is not currently supported");
}
LinkedNode tail = BuildList(sPrime[comptype]);
LinkedNode head = BuildTree(tail);
MemoryStream outputstream = new MemoryStream();
BitStream bitstream = new BitStream(data);
int decoded;
do
{
LinkedNode node = Decode(bitstream, head);
decoded = node.DecompressedValue;
switch (decoded)
{
case 256:
break;
case 257:
int newvalue = bitstream.ReadBits(8);
outputstream.WriteByte((byte)newvalue);
tail = InsertNode(tail, newvalue);
break;
default:
outputstream.WriteByte((byte)decoded);
break;
}
} while (decoded != 256);
outputstream.Seek(0, SeekOrigin.Begin);
return(outputstream);
}
public static MemoryStream Decompress(Stream data)
{
int decompressedValue;
int index = data.ReadByte();
if (index == 0)
{
throw new NotImplementedException("Compression type 0 is not currently supported");
}
LinkedNode tail = BuildList(sPrime[index]);
LinkedNode head = BuildTree(tail);
MemoryStream stream = new MemoryStream();
BitStream input = new BitStream(data);
do
{
decompressedValue = Decode(input, head).DecompressedValue;
switch (decompressedValue)
{
case 0x100:
break;
case 0x101:
{
int decomp = input.ReadBits(8);
stream.WriteByte((byte)decomp);
tail = InsertNode(tail, decomp);
break;
}
default:
stream.WriteByte((byte)decompressedValue);
break;
}
}while (decompressedValue != 0x100);
stream.Seek(0L, SeekOrigin.Begin);
return(stream);
}
private static LinkedNode Decode(BitStream input, LinkedNode head)
{
LinkedNode node = head;
while(node.Child0 != null)
{
int bit = input.ReadBits(1);
if (bit == -1)
throw new Exception("Unexpected end of file");
node = bit == 0 ? node.Child0 : node.Child1;
}
return node;
}
public static MemoryStream Decompress(Stream data)
{
int comptype = data.ReadByte();
if (comptype == 0)
throw new NotImplementedException("Compression type 0 is not currently supported");
LinkedNode tail = BuildList(sPrime[comptype]);
LinkedNode head = BuildTree(tail);
MemoryStream outputstream = new MemoryStream();
BitStream bitstream = new BitStream(data);
int decoded;
do
{
LinkedNode node = Decode(bitstream, head);
decoded = node.DecompressedValue;
switch(decoded)
{
case 256:
break;
case 257:
int newvalue = bitstream.ReadBits(8);
outputstream.WriteByte((byte)newvalue);
tail = InsertNode(tail, newvalue);
break;
default:
outputstream.WriteByte((byte)decoded);
break;
}
} while (decoded != 256);
outputstream.Seek(0, SeekOrigin.Begin);
return outputstream;
}