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128 lines
4.0 KiB
C#
128 lines
4.0 KiB
C#
// /***************************************************************************
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// Aaru Data Preservation Suite
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// ----------------------------------------------------------------------------
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//
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// Filename : AppleRle.cs
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// Author(s) : Natalia Portillo <claunia@claunia.com>
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//
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// Component : Compression algorithms.
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//
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// --[ Description ] ----------------------------------------------------------
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//
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// Decompress Apple variant of RLE.
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//
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// --[ License ] --------------------------------------------------------------
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//
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// This library is free software; you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as
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// published by the Free Software Foundation; either version 2.1 of the
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// License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License along with this library; if not, see <http://www.gnu.org/licenses/>.
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//
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// ----------------------------------------------------------------------------
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// Copyright © 2011-2021 Natalia Portillo
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// Copyright © 2018-2019 David Ryskalczyk
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// ****************************************************************************/
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using System.IO;
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namespace Aaru6.Compression
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{
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/// <summary>Implements the Apple version of RLE</summary>
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public class AppleRle
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{
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const uint DART_CHUNK = 20960;
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readonly Stream _inStream;
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int _count;
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bool _nextA; // true if A, false if B
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byte _repeatedByteA, _repeatedByteB;
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bool _repeatMode; // true if we're repeating, false if we're just copying
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/// <summary>Initializes a decompressor for the specified stream</summary>
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/// <param name="stream">Stream containing the compressed data</param>
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public AppleRle(Stream stream)
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{
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_inStream = stream;
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Reset();
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}
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void Reset()
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{
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_repeatedByteA = _repeatedByteB = 0;
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_count = 0;
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_nextA = true;
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_repeatMode = false;
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}
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/// <summary>Decompresses a byte</summary>
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/// <returns>Decompressed byte</returns>
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public int ProduceByte()
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{
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if(_repeatMode && _count > 0)
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{
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_count--;
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if(_nextA)
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{
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_nextA = false;
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return _repeatedByteA;
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}
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_nextA = true;
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return _repeatedByteB;
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}
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if(!_repeatMode &&
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_count > 0)
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{
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_count--;
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return _inStream.ReadByte();
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}
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if(_inStream.Position == _inStream.Length)
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return -1;
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while(true)
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{
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byte b1 = (byte)_inStream.ReadByte();
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byte b2 = (byte)_inStream.ReadByte();
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short s = (short)((b1 << 8) | b2);
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if(s == 0 ||
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s >= DART_CHUNK ||
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s <= -DART_CHUNK)
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continue;
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if(s < 0)
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{
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_repeatMode = true;
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_repeatedByteA = (byte)_inStream.ReadByte();
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_repeatedByteB = (byte)_inStream.ReadByte();
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_count = (-s * 2) - 1;
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_nextA = false;
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return _repeatedByteA;
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}
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if(s <= 0)
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continue;
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_repeatMode = false;
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_count = (s * 2) - 1;
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return _inStream.ReadByte();
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}
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}
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}
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} |