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* Lazily derive the huffman tables. Fix #839 * Lazy invoke fast table * Add performance tweaks to scan decoder. * Remove unneccessary classes.af/merge-core
James Jackson-South
7 years ago
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GitHub
GitHub
9 changed files with 212 additions and 189 deletions
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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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namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder |
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{ |
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internal unsafe struct FastACTable |
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{ |
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/// <summary>
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/// Gets the lookahead array
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/// </summary>
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public fixed short Lookahead[512]; |
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/// <summary>
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/// Derives a lookup table for fast AC entropy scan decoding.
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/// This can happen multiple times during progressive decoding but always outside mcu loops.
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/// </summary>
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/// <param name="huffmanTable">The AC Huffman table.</param>
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public void Derive(ref HuffmanTable huffmanTable) |
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{ |
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const int FastBits = ScanDecoder.FastBits; |
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ref short fastACRef = ref this.Lookahead[0]; |
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ref byte huffmanLookaheadRef = ref huffmanTable.Lookahead[0]; |
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ref byte huffmanValuesRef = ref huffmanTable.Values[0]; |
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ref short huffmanSizesRef = ref huffmanTable.Sizes[0]; |
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int i; |
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for (i = 0; i < (1 << FastBits); i++) |
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{ |
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byte fast = Unsafe.Add(ref huffmanLookaheadRef, i); |
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Unsafe.Add(ref fastACRef, i) = 0; |
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if (fast < byte.MaxValue) |
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{ |
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int rs = Unsafe.Add(ref huffmanValuesRef, fast); |
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int run = (rs >> 4) & 15; |
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int magbits = rs & 15; |
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int len = Unsafe.Add(ref huffmanSizesRef, fast); |
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if (magbits != 0 && len + magbits <= FastBits) |
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{ |
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// Magnitude code followed by receive_extend code
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int k = ((i << len) & ((1 << FastBits) - 1)) >> (FastBits - magbits); |
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int m = 1 << (magbits - 1); |
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if (k < m) |
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{ |
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k += (int)((~0U << magbits) + 1); |
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} |
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// If the result is small enough, we can fit it in fastAC table
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if (k >= -128 && k <= 127) |
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{ |
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Unsafe.Add(ref fastACRef, i) = (short)((k << 8) + (run << 4) + (len + magbits)); |
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} |
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} |
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} |
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} |
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} |
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} |
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} |
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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; |
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using System.Runtime.CompilerServices; |
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using SixLabors.ImageSharp.Memory; |
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using SixLabors.Memory; |
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namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder |
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{ |
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/// <summary>
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/// The collection of lookup tables used for fast AC entropy scan decoding.
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/// </summary>
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internal sealed class FastACTables : IDisposable |
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{ |
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private Buffer2D<short> tables; |
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/// <summary>
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/// Initializes a new instance of the <see cref="FastACTables"/> class.
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/// </summary>
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/// <param name="memoryAllocator">The memory allocator used to allocate memory for image processing operations.</param>
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public FastACTables(MemoryAllocator memoryAllocator) => this.tables = memoryAllocator.Allocate2D<short>(512, 4, AllocationOptions.Clean); |
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/// <summary>
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/// Gets the <see cref="Span{Int16}"/> representing the table at the index in the collection.
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/// </summary>
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/// <param name="index">The table index.</param>
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/// <returns><see cref="Span{Int16}"/></returns>
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[MethodImpl(InliningOptions.ShortMethod)] |
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public ReadOnlySpan<short> GetTableSpan(int index) => this.tables.GetRowSpan(index); |
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/// <summary>
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/// Gets a reference to the first element of the AC table indexed by <see cref="JpegComponent.ACHuffmanTableId"/>
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/// </summary>
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/// <param name="component">The frame component.</param>
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[MethodImpl(InliningOptions.ShortMethod)] |
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public ref short GetAcTableReference(JpegComponent component) => ref this.tables.GetRowSpan(component.ACHuffmanTableId)[0]; |
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/// <summary>
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/// Builds a lookup table for fast AC entropy scan decoding.
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/// </summary>
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/// <param name="index">The table index.</param>
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/// <param name="acHuffmanTables">The collection of AC Huffman tables.</param>
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public unsafe void BuildACTableLut(int index, HuffmanTables acHuffmanTables) |
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{ |
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const int FastBits = ScanDecoder.FastBits; |
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Span<short> fastAC = this.tables.GetRowSpan(index); |
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ref HuffmanTable huffmanTable = ref acHuffmanTables[index]; |
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int i; |
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for (i = 0; i < (1 << FastBits); i++) |
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{ |
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byte fast = huffmanTable.Lookahead[i]; |
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fastAC[i] = 0; |
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if (fast < byte.MaxValue) |
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{ |
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int rs = huffmanTable.Values[fast]; |
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int run = (rs >> 4) & 15; |
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int magbits = rs & 15; |
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int len = huffmanTable.Sizes[fast]; |
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if (magbits != 0 && len + magbits <= FastBits) |
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{ |
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// Magnitude code followed by receive_extend code
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int k = ((i << len) & ((1 << FastBits) - 1)) >> (FastBits - magbits); |
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int m = 1 << (magbits - 1); |
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if (k < m) |
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{ |
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k += (int)((~0U << magbits) + 1); |
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} |
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// if the result is small enough, we can fit it in fastAC table
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if (k >= -128 && k <= 127) |
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{ |
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fastAC[i] = (short)((k << 8) + (run << 4) + (len + magbits)); |
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} |
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} |
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} |
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} |
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} |
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/// <inheritdoc />
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public void Dispose() |
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{ |
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this.tables?.Dispose(); |
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this.tables = null; |
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} |
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} |
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} |
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@ -1,26 +0,0 @@ |
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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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namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder |
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{ |
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/// <summary>
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/// Defines a 2 pairs of huffman tables.
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/// </summary>
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internal sealed class HuffmanTables |
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{ |
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private readonly HuffmanTable[] tables = new HuffmanTable[4]; |
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/// <summary>
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/// Gets or sets the table at the given index.
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/// </summary>
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/// <param name="index">The index</param>
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/// <returns>The <see cref="HuffmanTable"/></returns>
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public ref HuffmanTable this[int index] |
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{ |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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get => ref this.tables[index]; |
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} |
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} |
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} |
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@ -0,0 +1,3 @@ |
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version https://git-lfs.github.com/spec/v1 |
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oid sha256:b37ac1cc34680db9721542ef5354f7509860afd37888a24f6350f29f5b63eea1 |
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size 397 |
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