public Memory <byte> DecompressGcz(Stream source, int length, int decompLength)
{
var props = new BemaniLzss2Properties
{
RingBufferOffset = 0xFFE,
RingBufferSize = 0x1000,
Type = BemaniLzss2Type.GCZ
};
return(Decompress(source, length, decompLength, props));
}
private Memory <byte> Decompress(Stream source, int length, int decompLength, BemaniLzss2Properties props)
{
var ring = new byte[props.RingBufferSize];
var ringPos = props.RingBufferOffset;
var controlWord = 1;
var controlBitsLeft = 0;
const int controlBitMask = 0x1;
if (decompLength <= 0)
{
decompLength = int.MaxValue;
}
var sourceReader = new BinaryReader(source);
var target = new MemoryStream();
var writer = new BinaryWriter(target);
using (var mem = new MemoryStream(sourceReader.ReadBytes(length)))
{
var reader = new BinaryReader(mem);
while (decompLength > 0 && length > 0)
{
if (controlBitsLeft == 0)
{
/* Read a control byte */
controlWord = reader.ReadByte();
length--;
controlBitsLeft = 8;
}
/* Decode a byte according to the current control byte bit */
if ((controlWord & controlBitMask) != 0)
{
/* Straight copy, store into history ring */
var data = reader.ReadByte();
length--;
writer.Write(data);
ring[ringPos] = data;
ringPos = (ringPos + 1) % props.RingBufferSize;
decompLength--;
}
else
{
/* Reference to data in ring buffer */
byte cmd2;
byte cmd1;
int chunkLength;
int chunkOffset;
switch (props.Type)
{
case BemaniLzss2Type.Firebeat:
cmd1 = reader.ReadByte();
cmd2 = reader.ReadByte();
length -= 2;
chunkLength = (cmd1 & 0x0F) + 3;
chunkOffset = ((cmd1 & 0xF0) << 4) + cmd2;
chunkOffset = ringPos - chunkOffset;
while (chunkOffset < 0)
{
chunkOffset += props.RingBufferSize;
}
break;
case BemaniLzss2Type.GCZ:
cmd1 = reader.ReadByte();
cmd2 = reader.ReadByte();
length -= 2;
chunkLength = (cmd2 & 0x0F) + 3;
chunkOffset = ((cmd2 & 0xF0) << 4) | cmd1;
break;
default:
return(target.AsMemory());
}
for (; chunkLength > 0 && length > 0; chunkLength--)
{
/* Copy historical data to output AND current ring pos */
writer.Write(ring[chunkOffset]);
ring[ringPos] = ring[chunkOffset];
/* Update counters */
chunkOffset = (chunkOffset + 1) % props.RingBufferSize;
ringPos = (ringPos + 1) % props.RingBufferSize;
decompLength--;
}
}
/* Get next control bit */
controlWord >>= 1;
controlBitsLeft--;
}
}
return(target.AsMemory());
}
