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Updating some readonly static data in JpegEncoderCore to take advanta…
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…ge of compiler functionality. (#855)
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@tannergooding @JimBobSquarePants
tannergooding authored and JimBobSquarePants committed Mar 26, 2019
1 parent 47e8f2c commit 5eb0122
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21 changes: 21 additions & 0 deletions src/ImageSharp/Common/Extensions/StreamExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// Licensed under the Apache License, Version 2.0.

using System;
using System.Buffers;
using System.IO;

using SixLabors.ImageSharp.Memory;
Expand Down Expand Up @@ -82,5 +83,25 @@ public static void Write(this Stream stream, IManagedByteBuffer buffer)
{
stream.Write(buffer.Array, 0, buffer.Length());
}

#if NET472 || NETSTANDARD1_3 || NETSTANDARD2_0
// This is a port of the CoreFX implementation and is MIT Licensed: https://github.com/dotnet/coreclr/blob/c4dca1072d15bdda64c754ad1ea474b1580fa554/src/System.Private.CoreLib/shared/System/IO/Stream.cs#L770
public static void Write(this Stream stream, ReadOnlySpan<byte> buffer)
{
// This uses ArrayPool<byte>.Shared, rather than taking a MemoryAllocator,
// in order to match the signature of the framework method that exists in
// .NET Core.
byte[] sharedBuffer = ArrayPool<byte>.Shared.Rent(buffer.Length);
try
{
buffer.CopyTo(sharedBuffer);
stream.Write(sharedBuffer, 0, buffer.Length);
}
finally
{
ArrayPool<byte>.Shared.Return(sharedBuffer);
}
}
#endif
}
}
185 changes: 103 additions & 82 deletions src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,85 +27,6 @@ internal sealed unsafe class JpegEncoderCore
/// </summary>
private const int QuantizationTableCount = 2;

/// <summary>
/// Counts the number of bits needed to hold an integer.
/// </summary>
private static readonly uint[] BitCountLut =
{
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5,
5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8,
};

/// <summary>
/// The SOS (Start Of Scan) marker "\xff\xda" followed by 12 bytes:
/// - the marker length "\x00\x0c",
/// - the number of components "\x03",
/// - component 1 uses DC table 0 and AC table 0 "\x01\x00",
/// - component 2 uses DC table 1 and AC table 1 "\x02\x11",
/// - component 3 uses DC table 1 and AC table 1 "\x03\x11",
/// - the bytes "\x00\x3f\x00". Section B.2.3 of the spec says that for
/// sequential DCTs, those bytes (8-bit Ss, 8-bit Se, 4-bit Ah, 4-bit Al)
/// should be 0x00, 0x3f, 0x00&lt;&lt;4 | 0x00.
/// </summary>
private static readonly byte[] SosHeaderYCbCr =
{
JpegConstants.Markers.XFF, JpegConstants.Markers.SOS,

// Marker
0x00, 0x0c,

// Length (high byte, low byte), must be 6 + 2 * (number of components in scan)
0x03, // Number of components in a scan, 3
0x01, // Component Id Y
0x00, // DC/AC Huffman table
0x02, // Component Id Cb
0x11, // DC/AC Huffman table
0x03, // Component Id Cr
0x11, // DC/AC Huffman table
0x00, // Ss - Start of spectral selection.
0x3f, // Se - End of spectral selection.
0x00

// Ah + Ah (Successive approximation bit position high + low)
};

/// <summary>
/// The unscaled quantization tables in zig-zag order. Each
/// encoder copies and scales the tables according to its quality parameter.
/// The values are derived from section K.1 after converting from natural to
/// zig-zag order.
/// </summary>
private static readonly byte[,] UnscaledQuant =
{
{
// Luminance.
16, 11, 12, 14, 12, 10, 16, 14, 13, 14, 18, 17, 16, 19, 24,
40, 26, 24, 22, 22, 24, 49, 35, 37, 29, 40, 58, 51, 61, 60,
57, 51, 56, 55, 64, 72, 92, 78, 64, 68, 87, 69, 55, 56, 80,
109, 81, 87, 95, 98, 103, 104, 103, 62, 77, 113, 121, 112,
100, 120, 92, 101, 103, 99,
},
{
// Chrominance.
17, 18, 18, 24, 21, 24, 47, 26, 26, 47, 99, 66, 56, 66,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
}
};

/// <summary>
/// A scratch buffer to reduce allocations.
/// </summary>
Expand Down Expand Up @@ -167,6 +88,103 @@ public JpegEncoderCore(IJpegEncoderOptions options)
this.subsample = options.Subsample;
}

/// <summary>
/// Gets the counts the number of bits needed to hold an integer.
/// </summary>
// The C# compiler emits this as a compile-time constant embedded in the PE file.
// This is effectively compiled down to: return new ReadOnlySpan<byte>(&data, length)
// More details can be found: https://github.com/dotnet/roslyn/pull/24621
private static ReadOnlySpan<byte> BitCountLut => new byte[]
{
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5,
5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8,
};

/// <summary>
/// Gets the SOS (Start Of Scan) marker "\xff\xda" followed by 12 bytes:
/// - the marker length "\x00\x0c",
/// - the number of components "\x03",
/// - component 1 uses DC table 0 and AC table 0 "\x01\x00",
/// - component 2 uses DC table 1 and AC table 1 "\x02\x11",
/// - component 3 uses DC table 1 and AC table 1 "\x03\x11",
/// - the bytes "\x00\x3f\x00". Section B.2.3 of the spec says that for
/// sequential DCTs, those bytes (8-bit Ss, 8-bit Se, 4-bit Ah, 4-bit Al)
/// should be 0x00, 0x3f, 0x00&lt;&lt;4 | 0x00.
/// </summary>
// The C# compiler emits this as a compile-time constant embedded in the PE file.
// This is effectively compiled down to: return new ReadOnlySpan<byte>(&data, length)
// More details can be found: https://github.com/dotnet/roslyn/pull/24621
private static ReadOnlySpan<byte> SosHeaderYCbCr => new byte[]
{
JpegConstants.Markers.XFF, JpegConstants.Markers.SOS,

// Marker
0x00, 0x0c,

// Length (high byte, low byte), must be 6 + 2 * (number of components in scan)
0x03, // Number of components in a scan, 3
0x01, // Component Id Y
0x00, // DC/AC Huffman table
0x02, // Component Id Cb
0x11, // DC/AC Huffman table
0x03, // Component Id Cr
0x11, // DC/AC Huffman table
0x00, // Ss - Start of spectral selection.
0x3f, // Se - End of spectral selection.
0x00

// Ah + Ah (Successive approximation bit position high + low)
};

/// <summary>
/// Gets the unscaled quantization tables in zig-zag order. Each
/// encoder copies and scales the tables according to its quality parameter.
/// The values are derived from section K.1 after converting from natural to
/// zig-zag order.
/// </summary>
// The C# compiler emits this as a compile-time constant embedded in the PE file.
// This is effectively compiled down to: return new ReadOnlySpan<byte>(&data, length)
// More details can be found: https://github.com/dotnet/roslyn/pull/24621
private static ReadOnlySpan<byte> UnscaledQuant_Luminance => new byte[]
{
// Luminance.
16, 11, 12, 14, 12, 10, 16, 14, 13, 14, 18, 17, 16, 19, 24,
40, 26, 24, 22, 22, 24, 49, 35, 37, 29, 40, 58, 51, 61, 60,
57, 51, 56, 55, 64, 72, 92, 78, 64, 68, 87, 69, 55, 56, 80,
109, 81, 87, 95, 98, 103, 104, 103, 62, 77, 113, 121, 112,
100, 120, 92, 101, 103, 99,
};

/// <summary>
/// Gets the unscaled quantization tables in zig-zag order. Each
/// encoder copies and scales the tables according to its quality parameter.
/// The values are derived from section K.1 after converting from natural to
/// zig-zag order.
/// </summary>
// The C# compiler emits this as a compile-time constant embedded in the PE file.
// This is effectively compiled down to: return new ReadOnlySpan<byte>(&data, length)
// More details can be found: https://github.com/dotnet/roslyn/pull/24621
private static ReadOnlySpan<byte> UnscaledQuant_Chrominance => new byte[]
{
// Chrominance.
17, 18, 18, 24, 21, 24, 47, 26, 26, 47, 99, 66, 56, 66,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
};

/// <summary>
/// Encode writes the image to the jpeg baseline format with the given options.
/// </summary>
Expand Down Expand Up @@ -259,9 +277,12 @@ private static void WriteDataToDqt(byte[] dqt, ref int offset, QuantIndex i, ref
/// <param name="quant">The quantization table.</param>
private static void InitQuantizationTable(int i, int scale, ref Block8x8F quant)
{
DebugGuard.MustBeBetweenOrEqualTo(i, 0, 1, nameof(i));
var unscaledQuant = (i == 0) ? UnscaledQuant_Luminance : UnscaledQuant_Chrominance;

for (int j = 0; j < Block8x8F.Size; j++)
{
int x = UnscaledQuant[i, j];
int x = unscaledQuant[j];
x = ((x * scale) + 50) / 100;
if (x < 1)
{
Expand Down Expand Up @@ -357,7 +378,7 @@ private void EmitHuffRLE(HuffIndex index, int runLength, int value)
}
else
{
bt = 8 + BitCountLut[a >> 8];
bt = 8 + (uint)BitCountLut[a >> 8];
}

this.EmitHuff(index, (int)((uint)(runLength << 4) | bt));
Expand Down Expand Up @@ -871,7 +892,7 @@ private void WriteStartOfScan<TPixel>(Image<TPixel> image)
{
// TODO: Need a JpegScanEncoder<TPixel> class or struct that encapsulates the scan-encoding implementation. (Similar to JpegScanDecoder.)
// TODO: We should allow grayscale writing.
this.outputStream.Write(SosHeaderYCbCr, 0, SosHeaderYCbCr.Length);
this.outputStream.Write(SosHeaderYCbCr);

switch (this.subsample)
{
Expand Down

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