Add benchmarks for Apple RLE decompression.

Aaru6.Compression/AppleRle.cs

@@ -0,0 +1,128 @@
+// /***************************************************************************
+// Aaru Data Preservation Suite
+// ----------------------------------------------------------------------------
+//
+// Filename       : AppleRle.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 © 2011-2021 Natalia Portillo
+// Copyright © 2018-2019 David Ryskalczyk
+// ****************************************************************************/
+
+using System.IO;
+
+namespace Aaru6.Compression
+{
+    /// <summary>Implements the Apple version of RLE</summary>
+    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
+
+        /// <summary>Initializes a decompressor for the specified stream</summary>
+        /// <param name="stream">Stream containing the compressed data</param>
+        public AppleRle(Stream stream)
+        {
+            _inStream = stream;
+            Reset();
+        }
+
+        void Reset()
+        {
+            _repeatedByteA = _repeatedByteB = 0;
+            _count         = 0;
+            _nextA         = true;
+            _repeatMode    = false;
+        }
+
+        /// <summary>Decompresses a byte</summary>
+        /// <returns>Decompressed byte</returns>
+        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();
+            }
+        }
+    }
+}