1 files changed, 105 insertions, 0 deletions
diff --git a/Ryujinx.HLE/Loaders/Compression/BackwardsLz.cs b/Ryujinx.HLE/Loaders/Compression/BackwardsLz.cs
new file mode 100644
index 00000000..43cc601f
--- /dev/null
+++ b/Ryujinx.HLE/Loaders/Compression/BackwardsLz.cs
@@ -0,0 +1,105 @@
+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;
+        }
+    }
+}
+\ No newline at end of file