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ryujinx-fork/Ryujinx.HLE/Loaders/Compression/BackwardsLz.cs

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using System;
using System.IO;
namespace Ryujinx.HLE.Loaders.Compression
{
static class BackwardsLz
{
private class BackwardsReader
{
private Stream BaseStream;
public BackwardsReader(Stream BaseStream)
{
this.BaseStream = BaseStream;
}
public byte ReadByte()
{
BaseStream.Seek(-1, SeekOrigin.Current);
byte Value = (byte)BaseStream.ReadByte();
BaseStream.Seek(-1, SeekOrigin.Current);
return Value;
}
public short ReadInt16()
{
return (short)((ReadByte() << 8) | (ReadByte() << 0));
}
public int ReadInt32()
{
return ((ReadByte() << 24) |
(ReadByte() << 16) |
(ReadByte() << 8) |
(ReadByte() << 0));
}
}
public static byte[] Decompress(Stream Input, int DecompressedLength)
{
long End = Input.Position;
BackwardsReader Reader = new BackwardsReader(Input);
int AdditionalDecLength = Reader.ReadInt32();
int StartOffset = Reader.ReadInt32();
int CompressedLength = Reader.ReadInt32();
Input.Seek(12 - StartOffset, SeekOrigin.Current);
byte[] Dec = new byte[DecompressedLength];
int DecompressedLengthUnpadded = CompressedLength + AdditionalDecLength;
int DecompressionStart = DecompressedLength - DecompressedLengthUnpadded;
int DecPos = Dec.Length;
byte Mask = 0;
byte Header = 0;
while (DecPos > DecompressionStart)
{
if ((Mask >>= 1) == 0)
{
Header = Reader.ReadByte();
Mask = 0x80;
}
if ((Header & Mask) == 0)
{
Dec[--DecPos] = Reader.ReadByte();
}
else
{
ushort Pair = (ushort)Reader.ReadInt16();
int Length = (Pair >> 12) + 3;
int Position = (Pair & 0xfff) + 3;
DecPos -= Length;
if (Length <= Position)
{
int SrcPos = DecPos + Position;
Buffer.BlockCopy(Dec, SrcPos, Dec, DecPos, Length);
}
else
{
for (int Offset = 0; Offset < Length; Offset++)
{
Dec[DecPos + Offset] = Dec[DecPos + Position + Offset];
}
}
}
}
return Dec;
}
}
}