private static ReadBuffer UnpackSequences(ReadBuffer packedData, byte seqMarker)
{
var remaining = packedData;
var result = new WriteBuffer();
while (remaining.Length > 0)
{
var value = remaining[0];
remaining = remaining.Drop(1);
if (value != seqMarker)
{
result.Append(value);
}
else
{
var sequence = remaining.TakeUntil(seqMarker);
var count = remaining[sequence.Length + 1];
for (int i = 0; i < count; i++)
{
result.Append(sequence);
}
remaining = remaining.Drop(sequence.Length + 2);
}
}
return(result.ToReadBuffer());
}
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());
}
