🐛Implement Apple RLE algorithm, fix #120, thanks to David Ryskalczyk.

DiscImageChef.Compression/AppleRle.cs

@@ -0,0 +1,112 @@
+// /***************************************************************************
+// The Disc Image Chef
+// ----------------------------------------------------------------------------
+//
+// Filename       : TeleDiskLzh.cs
+// Author(s)      : Natalia Portillo <claunia@claunia.com>
+//
+// Component      : Compression algorithms.
+//
+// --[ Description ] ----------------------------------------------------------
+//
+//     Decompress Apple variant of RLE.
+//
+// --[ License ] --------------------------------------------------------------
+//
+//     This library is free software; you can redistribute it and/or modify
+//     it under the terms of the GNU Lesser General Public License as
+//     published by the Free Software Foundation; either version 2.1 of the
+//     License, or (at your option) any later version.
+//
+//     This library is distributed in the hope that it will be useful, but
+//     WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+//     Lesser General Public License for more details.
+//
+//     You should have received a copy of the GNU Lesser General Public
+//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
+//
+// ----------------------------------------------------------------------------
+// Copyright © 2011-2018 Natalia Portillo
+// Copyright © 2018 David Ryskalczyk
+// ****************************************************************************/
+
+using System.IO;
+
+namespace DiscImageChef.Compression
+{
+    public class AppleRle
+    {
+        const uint DART_CHUNK = 20960;
+
+        readonly Stream inStream;
+        int             count;
+        bool            nextA; // true if A, false if B
+
+        byte repeatedbyteA, repeatedbyteB;
+        bool repeatMode; // true if we're repeating, false if we're just copying
+
+        public AppleRle(Stream stream)
+        {
+            inStream = stream;
+            Reset();
+        }
+
+        void Reset()
+        {
+            repeatedbyteA = repeatedbyteB = 0;
+            count         = 0;
+            nextA         = true;
+            repeatMode    = false;
+        }
+
+        public int ProduceByte()
+        {
+            if(repeatMode && count > 0)
+            {
+                count--;
+                if(nextA)
+                {
+                    nextA = false;
+                    return repeatedbyteA;
+                }
+
+                nextA = true;
+                return repeatedbyteB;
+            }
+
+            if(!repeatMode && count > 0)
+            {
+                count--;
+                return inStream.ReadByte();
+            }
+
+            if(inStream.Position == inStream.Length) return -1;
+
+            while(true)
+            {
+                byte  b1 = (byte)inStream.ReadByte();
+                byte  b2 = (byte)inStream.ReadByte();
+                short s  = (short)((b1 << 8) | b2);
+
+                if(s == 0 || s >= DART_CHUNK || s <= -DART_CHUNK) continue;
+
+                if(s < 0)
+                {
+                    repeatMode    = true;
+                    repeatedbyteA = (byte)inStream.ReadByte();
+                    repeatedbyteB = (byte)inStream.ReadByte();
+                    count         = -s * 2 - 1;
+                    nextA         = false;
+                    return repeatedbyteA;
+                }
+
+                if(s <= 0) continue;
+
+                repeatMode = false;
+                count      = s * 2 - 1;
+                return inStream.ReadByte();
+            }
+        }
+    }
+}