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Ryujinx/Ryujinx.HLE/Loaders/Compression/BackwardsLz.cs

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C#
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using System;
namespace Ryujinx.HLE.Loaders.Compression
{
static class BackwardsLz
{
private class BackwardsReader
{
private byte[] _data;
private int _position;
public int Position => _position;
public BackwardsReader(byte[] data, int end)
{
_data = data;
_position = end;
}
public void SeekCurrent(int offset)
{
_position += offset;
}
public byte ReadByte()
{
return _data[--_position];
}
public short ReadInt16()
{
return (short)((ReadByte() << 8) | (ReadByte() << 0));
}
public int ReadInt32()
{
return ((ReadByte() << 24) |
(ReadByte() << 16) |
(ReadByte() << 8) |
(ReadByte() << 0));
}
}
public static void DecompressInPlace(byte[] buffer, int headerEnd)
{
BackwardsReader reader = new BackwardsReader(buffer, headerEnd);
int additionalDecLength = reader.ReadInt32();
int startOffset = reader.ReadInt32();
int compressedLength = reader.ReadInt32();
reader.SeekCurrent(12 - startOffset);
int decBase = headerEnd - compressedLength;
int decPos = compressedLength + additionalDecLength;
byte mask = 0;
byte header = 0;
while (decPos > 0)
{
if ((mask >>= 1) == 0)
{
header = reader.ReadByte();
mask = 0x80;
}
if ((header & mask) == 0)
{
buffer[decBase + --decPos] = reader.ReadByte();
}
else
{
ushort pair = (ushort)reader.ReadInt16();
int length = (pair >> 12) + 3;
int position = (pair & 0xfff) + 3;
if (length > decPos)
{
length = decPos;
}
decPos -= length;
int dstPos = decBase + decPos;
if (length <= position)
{
int srcPos = dstPos + position;
Buffer.BlockCopy(buffer, srcPos, buffer, dstPos, length);
}
else
{
for (int offset = 0; offset < length; offset++)
{
buffer[dstPos + offset] = buffer[dstPos + position + offset];
}
}
}
}
}
}
}