public static void Decompress(CompressionHeader header, MemoryMappedViewAccessor original,
MemoryMappedViewAccessor uncompressed)
{
switch (header.Compression)
{
case CompressionType.LZ77:
case CompressionType.ExtendedLZ77:
LZ77.Expand(header, original, uncompressed);
break;
default:
throw new ArgumentException($"{header.Compression} is not properly supported.");
}
}
/// <summary>
/// Uncompresses a valid LZ77 file.
/// </summary>
/// <param name="header">The compression header of the original file.</param>
/// <param name="original">The original file accessor.</param>
/// <param name="uncompressed">The uncompressed file accessor to write to.</param>
public static void Expand(CompressionHeader header, MemoryMappedViewAccessor original, MemoryMappedViewAccessor uncompressed)
{
var extended = header.Compression == CompressionType.ExtendedLZ77;
var uncompLen = uncompressed.Capacity;
long origPos = header.HeaderSize;
long uncompPos = 0;
while (uncompPos < uncompLen)
{
byte bit = 8;
var control = original.ReadByte(origPos++);
while (bit-- != 0 && uncompPos < uncompLen)
{
if ((control & (1 << bit)) == 0)
{
uncompressed.Write(uncompPos++, original.ReadByte(origPos++));
}
else
{
var temp = original.ReadByte(origPos) >> 4;
var num = !extended
? temp + 3
: temp == 1
? (((original.ReadByte(origPos++) & 0x0F) << 12) | (original.ReadByte(origPos++) << 4) |
(original.ReadByte(origPos) >> 4)) + 0xFF + 0xF + 3
: temp == 0
? (((original.ReadByte(origPos++) & 0x0F) << 4) |
(original.ReadByte(origPos) >> 4)) + 0xF + 2
: temp + 1;
var offset = (((original.ReadByte(origPos++) & 0xF) << 8) | original.ReadByte(origPos++)) + 2;
while (uncompPos != uncompLen && num-- > 0)
{
uncompressed.Write(uncompPos++, uncompressed.ReadByte(uncompPos - offset));
}
}
}
}
}
