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JimBobSquarePantsJimBobSquarePants
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Faster Jpeg Huffman Decoding. (#894)
* Read from underlying stream less often * Update benchmark dependencies * Experimental mango port Currently broken * Populate table, 64byte buffer Still broken. * Baseline, non RST works * 15/19 baseline tests pass now. * Optimize position change. * 18/19 pass * 19/19 baseline decoded * Can now decode all images. * Now faster and much cleaner. * Cleanup * Fix reader, update benchmarks * Update dependencies * Remove unused method * No need to clean initial buffer * Remove bounds check on ReadByte() * Refactor from feedback
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‎src/ImageSharp.Drawing/ImageSharp.Drawing.csproj‎

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<AdditionalFiles Include="..\..\standards\stylecop.json" />
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<PackageReference Include="SixLabors.Fonts" Version="1.0.0-beta0008" />
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<PackageReference Include="SixLabors.Shapes" Version="1.0.0-beta0008" />
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<PackageReference Include="StyleCop.Analyzers" Version="1.1.1-beta.61" PrivateAssets="All" />
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<PackageReference Include="StyleCop.Analyzers" Version="1.1.1-rc.114" PrivateAssets="All" />
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</ItemGroup>
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<PropertyGroup>

‎src/ImageSharp/Formats/Jpeg/Components/Decoder/FastACTable.cs‎

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‎src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanBuffer.cs‎

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// Copyright (c) Six Labors and contributors.
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// Licensed under the Apache License, Version 2.0.
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using System.Runtime.CompilerServices;
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using SixLabors.ImageSharp.IO;
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namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
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{
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/// <summary>
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/// Used to buffer and track the bits read from the Huffman entropy encoded data.
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/// </summary>
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internal struct HuffmanScanBuffer
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{
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private readonly DoubleBufferedStreamReader stream;
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// The entropy encoded code buffer.
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private ulong data;
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// The number of valid bits left to read in the buffer.
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private int remain;
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// Whether there is more data to pull from the stream for the current mcu.
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private bool noMore;
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public HuffmanScanBuffer(DoubleBufferedStreamReader stream)
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{
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this.stream = stream;
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this.data = 0ul;
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this.remain = 0;
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this.Marker = JpegConstants.Markers.XFF;
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this.MarkerPosition = 0;
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this.BadMarker = false;
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this.noMore = false;
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this.Eof = false;
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}
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/// <summary>
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/// Gets or sets the current, if any, marker in the input stream.
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/// </summary>
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public byte Marker { get; set; }
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/// <summary>
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/// Gets or sets the opening position of an identified marker.
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/// </summary>
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public long MarkerPosition { get; set; }
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/// <summary>
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/// Gets or sets a value indicating whether we have a bad marker, I.E. One that is not between RST0 and RST7
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/// </summary>
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public bool BadMarker { get; set; }
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/// <summary>
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/// Gets or sets a value indicating whether we have prematurely reached the end of the file.
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/// </summary>
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public bool Eof { get; set; }
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[MethodImpl(InliningOptions.ShortMethod)]
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public void CheckBits()
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{
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if (this.remain < 16)
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{
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this.FillBuffer();
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}
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public void Reset()
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{
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this.data = 0ul;
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this.remain = 0;
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this.Marker = JpegConstants.Markers.XFF;
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this.MarkerPosition = 0;
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this.BadMarker = false;
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this.noMore = false;
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this.Eof = false;
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public bool HasRestart()
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{
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byte m = this.Marker;
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return m >= JpegConstants.Markers.RST0 && m <= JpegConstants.Markers.RST7;
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public void FillBuffer()
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{
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// Attempt to load at least the minimum number of required bits into the buffer.
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// We fail to do so only if we hit a marker or reach the end of the input stream.
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this.remain += 48;
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this.data = (this.data << 48) | this.GetBytes();
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public unsafe int DecodeHuffman(ref HuffmanTable h)
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{
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this.CheckBits();
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int v = this.PeekBits(JpegConstants.Huffman.LookupBits);
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int symbol = h.LookaheadValue[v];
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int size = h.LookaheadSize[v];
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if (size == JpegConstants.Huffman.SlowBits)
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{
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ulong x = this.data << (JpegConstants.Huffman.RegisterSize - this.remain);
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while (x > h.MaxCode[size])
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{
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size++;
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}
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v = (int)(x >> (JpegConstants.Huffman.RegisterSize - size));
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symbol = h.Values[h.ValOffset[size] + v];
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}
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this.remain -= size;
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return symbol;
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public int Receive(int nbits)
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{
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this.CheckBits();
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return Extend(this.GetBits(nbits), nbits);
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}
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[MethodImpl(InliningOptions.ShortMethod)]
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public int GetBits(int nbits) => (int)ExtractBits(this.data, this.remain -= nbits, nbits);
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[MethodImpl(InliningOptions.ShortMethod)]
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public int PeekBits(int nbits) => (int)ExtractBits(this.data, this.remain - nbits, nbits);
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[MethodImpl(InliningOptions.ShortMethod)]
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private static ulong ExtractBits(ulong value, int offset, int size) => (value >> offset) & (ulong)((1 << size) - 1);
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[MethodImpl(InliningOptions.ShortMethod)]
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private static int Extend(int v, int nbits) => v - ((((v + v) >> nbits) - 1) & ((1 << nbits) - 1));
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[MethodImpl(InliningOptions.ShortMethod)]
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private ulong GetBytes()
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{
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ulong temp = 0;
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for (int i = 0; i < 6; i++)
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{
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int b = this.noMore ? 0 : this.stream.ReadByte();
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if (b == -1)
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{
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// We've encountered the end of the file stream which means there's no EOI marker in the image
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// or the SOS marker has the wrong dimensions set.
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this.Eof = true;
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b = 0;
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}
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// Found a marker.
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if (b == JpegConstants.Markers.XFF)
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{
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this.MarkerPosition = this.stream.Position - 1;
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int c = this.stream.ReadByte();
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while (c == JpegConstants.Markers.XFF)
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{
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c = this.stream.ReadByte();
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if (c == -1)
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{
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this.Eof = true;
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c = 0;
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break;
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}
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}
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if (c != 0)
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{
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this.Marker = (byte)c;
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this.noMore = true;
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if (!this.HasRestart())
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{
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this.BadMarker = true;
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}
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}
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}
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temp = (temp << 8) | (ulong)(long)b;
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}
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return temp;
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}
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}
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}

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