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

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2.9 KiB
C#
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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)
{
_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;
}
}
}