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Change Apple RLE algorithm for a faster version.

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This commit is contained in:
Natalia Portillo
2021-10-17 01:12:06 +01:00
parent 3e30153b6c
commit bc2a7acea5
4 changed files with 77 additions and 81 deletions
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120
Aaru6.Compression/AppleRle.cs
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@@ -31,8 +31,6 @@
// Copyright © 2018-2019 David Ryskalczyk
// ****************************************************************************/
using System.IO;
namespace Aaru6.Compression
{
/// <summary>Implements the Apple version of RLE</summary>
@@ -40,63 +38,57 @@ namespace Aaru6.Compression
{
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)
/// <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)
{
_inStream = stream;
Reset();
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;
}
void Reset()
{
_repeatedByteA = _repeatedByteB = 0;
_count = 0;
_nextA = true;
_repeatMode = false;
nextA = true;
destination[outPosition++] = repeatedByteB;
continue;
}
case false when count > 0:
count--;
destination[outPosition++] = source[inPosition++];
continue;
}
/// <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;
if(inPosition == source.Length)
break;
while(true)
{
byte b1 = (byte)_inStream.ReadByte();
byte b2 = (byte)_inStream.ReadByte();
byte b1 = source[inPosition++];
byte b2 = source[inPosition++];
short s = (short)((b1 << 8) | b2);
if(s == 0 ||
@@ -106,23 +98,27 @@ namespace Aaru6.Compression
if(s < 0)
{
_repeatMode = true;
_repeatedByteA = (byte)_inStream.ReadByte();
_repeatedByteB = (byte)_inStream.ReadByte();
_count = (-s * 2) - 1;
_nextA = false;
repeatMode = true;
repeatedByteA = source[inPosition++];
repeatedByteB = source[inPosition++];
count = (-s * 2) - 1;
nextA = false;
return _repeatedByteA;
destination[outPosition++] = repeatedByteA;
break;
}
if(s <= 0)
continue;
repeatMode = false;
count = (s * 2) - 1;
_repeatMode = false;
_count = (s * 2) - 1;
destination[outPosition++] = source[inPosition++];
return _inStream.ReadByte();
break;
}
}
return outPosition;
}
}
}

4
AaruBenchmark/Benchs.cs
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@@ -12,7 +12,7 @@ namespace AaruBenchmark
public void Aaru() => Compression.Aaru.AppleRle();
[Benchmark]
public void Aaru6() => Compression.Aaru6.AppleRle();
public void Aaru6() => Aaru6Compressions.AppleRle();
}
[SimpleJob(RuntimeMoniker.Net60)]
@@ -22,7 +22,7 @@ namespace AaruBenchmark
public void Aaru() => Compression.Aaru.TeleDiskLzh();
[Benchmark]
public void Aaru6() => Compression.Aaru6.TeleDiskLzh();
public void Aaru6() => Aaru6Compressions.TeleDiskLzh();
}
[SimpleJob(RuntimeMoniker.Net60)]

12
AaruBenchmark/Compression/Aaru6.cs → AaruBenchmark/Compression/Aaru6Compressions.cs
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@@ -4,11 +4,11 @@ using Aaru6.Compression;
namespace AaruBenchmark.Compression
{
public class Aaru6
public class Aaru6Compressions
{
public static void AppleRle()
{
const int bufferSize = 20960;
const int bufferSize = 32768;
byte[] input = new byte[1102];
var fs = new FileStream(Path.Combine(Program.Folder, "apple_rle.bin"), FileMode.Open, FileAccess.Read);
@@ -19,12 +19,12 @@ namespace AaruBenchmark.Compression
byte[] output = new byte[bufferSize];
var rle = new AppleRle(new MemoryStream(input));
int realSize = Aaru6.Compression.AppleRle.DecodeBuffer(input, output);
for(int i = 0; i < bufferSize; i++)
output[i] = (byte)rle.ProduceByte();
if(realSize != 20960)
throw new InvalidDataException("Incorrect decompressed size");
string crc = Crc32Context.Data(output, out _);
string crc = Crc32Context.Data(output, (uint)realSize, out _);
if(crc != "3525ef06")
throw new InvalidDataException("Incorrect decompressed checksum");

BIN
Benchmarks.ods
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