Aaru/Aaru.Compression/AppleRle.cs

// /***************************************************************************
// 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.Runtime.InteropServices;

namespace Aaru.Compression
{
    /// <summary>Implements the Apple version of RLE</summary>
    public static class AppleRle
    {
        [DllImport("libAaru.Compression.Native", SetLastError = true)]
        static extern int AARU_apple_rle_decode_buffer(byte[] dst_buffer, int dst_size, byte[] src_buffer, int src_size);

        const uint DART_CHUNK = 20960;

        /// <summary>Decodes a buffer compressed with Apple RLE</summary>
        /// <param name="source">Encoded buffer</param>
        /// <param name="destination">Buffer where to write the decoded data</param>
        /// <returns>The number of decoded bytes</returns>
        public static int DecodeBuffer(byte[] source, byte[] destination)
        {
            if(Native.IsSupported)
                return AARU_apple_rle_decode_buffer(destination, destination.Length, source, source.Length);

            int  count         = 0;
            bool nextA         = true; // true if A, false if B
            byte repeatedByteA = 0, repeatedByteB = 0;
            bool repeatMode    = false; // true if we're repeating, false if we're just copying
            int  inPosition    = 0, outPosition = 0;

            while(inPosition  <= source.Length &&
                  outPosition <= destination.Length)
            {
                switch(repeatMode)
                {
                    case true when count > 0:
                    {
                        count--;

                        if(nextA)
                        {
                            nextA = false;

                            destination[outPosition++] = repeatedByteA;

                            continue;
                        }

                        nextA = true;

                        destination[outPosition++] = repeatedByteB;

                        continue;
                    }
                    case false when count > 0:
                        count--;

                        destination[outPosition++] = source[inPosition++];

                        continue;
                }

                if(inPosition == source.Length)
                    break;

                while(true)
                {
                    byte  b1 = source[inPosition++];
                    byte  b2 = source[inPosition++];
                    short s  = (short)((b1 << 8) | b2);

                    if(s == 0          ||
                       s >= DART_CHUNK ||
                       s <= -DART_CHUNK)
                        continue;

                    if(s < 0)
                    {
                        repeatMode    = true;
                        repeatedByteA = source[inPosition++];
                        repeatedByteB = source[inPosition++];
                        count         = (-s * 2) - 1;
                        nextA         = false;

                        destination[outPosition++] = repeatedByteA;

                        break;
                    }

                    repeatMode = false;
                    count      = (s * 2) - 1;

                    destination[outPosition++] = source[inPosition++];

                    break;
                }
            }

            return outPosition;
        }
    }
}