AaruBenchmark/Aaru6.Compression/ADC.cs

//
// ADC.cs
//
// Author:
//       Natalia Portillo <claunia@claunia.com>
//
// Copyright (c) 2016-2023 Natalia Portillo
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

using System.Runtime.CompilerServices;

namespace Aaru6.Compression;

/// <summary>Implements the Apple version of RLE</summary>
public class ADC
{
    const int PLAIN      = 1;
    const int TWO_BYTE   = 2;
    const int THREE_BYTE = 3;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetChunkType(byte byt) => (byt & 0x80) == 0x80
                                             ? PLAIN
                                             : (byt & 0x40) == 0x40
                                                 ? THREE_BYTE
                                                 : TWO_BYTE;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetChunkSize(byte byt) => GetChunkType(byt) switch
                                         {
                                             PLAIN      => (byt & 0x7F)        + 1,
                                             TWO_BYTE   => ((byt & 0x3F) >> 2) + 3,
                                             THREE_BYTE => (byt & 0x3F)        + 4,
                                             _          => -1
                                         };

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetOffset(ReadOnlySpan<byte> chunk) => GetChunkType(chunk[0]) switch
                                                      {
                                                          PLAIN      => 0,
                                                          TWO_BYTE   => ((chunk[0] & 0x03) << 8) + chunk[1],
                                                          THREE_BYTE => (chunk[1]          << 8) + chunk[2],
                                                          _          => -1
                                                      };

    /// <summary>Decompresses a byte buffer that's compressed with ADC</summary>
    /// <param name="source">Compressed buffer</param>
    /// <param name="destination">Buffer to hold decompressed data</param>
    /// <returns>How many bytes are stored on <paramref name="destination" /></returns>
    [MethodImpl(MethodImplOptions.AggressiveOptimization)]
    public static int DecodeBuffer(byte[] source, byte[] destination)
    {
        var        inputPosition = 0;
        int        chunkSize;
        int        offset;
        int        chunkType;
        var        outPosition = 0;
        Span<byte> temp        = stackalloc byte[3];

        while(inputPosition < source.Length)
        {
            byte readByte = source[inputPosition++];

            chunkType = GetChunkType(readByte);

            switch(chunkType)
            {
                case PLAIN:
                    chunkSize = GetChunkSize(readByte);

                    if(outPosition + chunkSize > destination.Length)
                        goto finished;

                    Array.Copy(source, inputPosition, destination, outPosition, chunkSize);
                    outPosition   += chunkSize;
                    inputPosition += chunkSize;

                    break;
                case TWO_BYTE:
                    chunkSize = GetChunkSize(readByte);
                    temp[0]   = readByte;
                    temp[1]   = source[inputPosition++];
                    offset    = GetOffset(temp);

                    if(outPosition + chunkSize > destination.Length)
                        goto finished;

                    if(offset == 0)
                    {
                        byte lastByte = destination[outPosition - 1];

                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = lastByte;
                            outPosition++;
                        }
                    }
                    else
                    {
                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = destination[outPosition - offset - 1];
                            outPosition++;
                        }
                    }

                    break;
                case THREE_BYTE:
                    chunkSize = GetChunkSize(readByte);
                    temp[0]   = readByte;
                    temp[1]   = source[inputPosition++];
                    temp[2]   = source[inputPosition++];
                    offset    = GetOffset(temp);

                    if(outPosition + chunkSize > destination.Length)
                        goto finished;

                    if(offset == 0)
                    {
                        byte lastByte = destination[outPosition - 1];

                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = lastByte;
                            outPosition++;
                        }
                    }
                    else
                    {
                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = destination[outPosition - offset - 1];
                            outPosition++;
                        }
                    }

                    break;
            }
        }

    finished:

        return outPosition;
    }
}