private static ReadBuffer UnpackPass(ReadBuffer packedData)
{
switch (packedData[0])
{
case 1:
return(UnpackRLE(packedData.Drop(8)));
case 2:
return(UnpackVLE(packedData.Drop(4)));
default:
throw new ArgumentException("Unknown compression type!");
}
}
public static byte[] Unpack(byte[] packedData)
{
var buffer = new ReadBuffer(packedData);
bool singlePass = (buffer[0] & 0x80) == 0;
int passCount = singlePass ? 1 : buffer[0] & 0x7f;
ReadBuffer currentPass = singlePass ? buffer : buffer.Drop(4);
for (int i = 0; i < passCount; i++)
{
currentPass = UnpackPass(currentPass);
}
return(currentPass.ToArray());
}
private static ReadBuffer UnpackRLE(ReadBuffer packedData)
{
int escCount = packedData[0] & 0x7f;
var escCodes = packedData.Slice(1, escCount);
var rleData = packedData.Drop(escCount + 1);
var escLookup = new byte[0x100];
for (int i = 0; i < escCount; i++)
{
escLookup[escCodes[i]] = (byte)(i + 1);
}
bool compressed = (packedData[0] & 0x80) == 0;
var encodedData = compressed ? UnpackSequences(rleData, escCodes[1]) : rleData;
var result = new WriteBuffer();
while (encodedData.Length > 0)
{
var code = escLookup[encodedData[0]];
switch (code)
{
case 0:
result.Append(encodedData[0]);
encodedData = encodedData.Drop(1);
break;
case 1:
result.AppendRepeat(encodedData[2], encodedData[1]);
encodedData = encodedData.Drop(3);
break;
case 3:
result.AppendRepeat(encodedData[3], encodedData[1] + (((int)encodedData[2]) << 8));
encodedData = encodedData.Drop(4);
break;
default:
result.AppendRepeat(encodedData[1], code - 1);
encodedData = encodedData.Drop(2);
break;
}
}
return(result.ToReadBuffer());
}
private static ReadBuffer UnpackVLE(ReadBuffer packedData)
{
var widthsCount = packedData[0];
var widths = packedData.Slice(1, widthsCount);
var alphabetCount = widths.Select(val => (int)val).Sum();
var alphabet = packedData.Slice(1 + widthsCount, alphabetCount);
var dictionary = new HuffmanTree(widths, alphabet);
var stream = EnumerateBits(packedData.Drop(1 + widthsCount + alphabetCount));
var result = new WriteBuffer();
while (true)
{
int value = dictionary.DecodeByte(stream);
if (value < 0)
{
break;
}
result.Append((byte)value);
}
return(result.ToReadBuffer());
}
