Respond to Anton fedback

src/ImageSharp/Common/Helpers/SimdUtils.cs

@@ -25,6 +25,13 @@ namespace SixLabors.ImageSharp
         public static bool HasVector8 { get; } =
             Vector.IsHardwareAccelerated && Vector<float>.Count == 8 && Vector<int>.Count == 8;
 
+        /// <summary>
+        /// Gets a value indicating whether <see cref="Vector{T}"/> code is being JIT-ed to SSE instructions
+        /// where float and integer registers are of size 128 byte.
+        /// </summary>
+        public static bool HasVector4 { get; } =
+            Vector.IsHardwareAccelerated && Vector<float>.Count == 4;
+
         public static bool HasAvx2
         {
             get

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.Avx2JpegColorConverter.cs

@@ -1,10 +1,6 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
-#if SUPPORTS_RUNTIME_INTRINSICS
-using System.Runtime.Intrinsics.X86;
-#endif
-
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
 {
     internal abstract partial class JpegColorConverter

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromCmykAvx2.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromYCbCrVector.cs → src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromYCbCrVector4.cs

@@ -11,14 +11,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
 {
     internal abstract partial class JpegColorConverter
     {
-        internal sealed class FromYCbCrVector : VectorizedJpegColorConverter
+        internal sealed class FromYCbCrVector4 : VectorizedJpegColorConverter
         {
-            public FromYCbCrVector(int precision)
+            public FromYCbCrVector4(int precision)
                 : base(JpegColorSpace.YCbCr, precision, 8)
             {
             }
 
-            protected override bool IsAvailable => true;
+            protected override bool IsAvailable => SimdUtils.HasVector4;
 
             protected override void ConvertCoreVectorized(in ComponentValues values, Span<Vector4> result)
             {
@@ -74,7 +74,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                     tmp.MultiplyInplace(1.772F);
                     b.AddInplace(ref tmp);
 
-                    if (Vector<float>.Count == 4)
+                    if (SimdUtils.HasVector4)
                     {
                         // TODO: Find a way to properly run & test this path on AVX2 PC-s! (Have I already mentioned that Vector<T> is terrible?)
                         r.RoundAndDownscalePreVector8(maxValue);

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.cs

@@ -62,8 +62,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// </summary>
         public static JpegColorConverter GetConverter(JpegColorSpace colorSpace, int precision)
         {
-            JpegColorConverter converter = Array.Find(Converters, c => c.ColorSpace == colorSpace
-                                                                    && c.Precision == precision);
+            JpegColorConverter converter = Array.Find(
+                Converters,
+                c => c.ColorSpace == colorSpace
+                && c.Precision == precision);
 
             if (converter is null)
             {
@@ -94,7 +96,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
             converters.AddRange(GetGrayScaleConverters(8));
             converters.AddRange(GetRgbConverters(8));
 
-            // 8-bit converters
+            // 12-bit converters
             converters.AddRange(GetYCbCrConverters(12));
             converters.AddRange(GetYccKConverters(12));
             converters.AddRange(GetCmykConverters(12));
@@ -109,9 +111,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// </summary>
         private static IEnumerable<JpegColorConverter> GetYCbCrConverters(int precision)
         {
+#if SUPPORTS_RUNTIME_INTRINSICS
             yield return new FromYCbCrAvx2(precision);
+#endif
             yield return new FromYCbCrVector8(precision);
-            yield return new FromYCbCrVector(precision);
+            yield return new FromYCbCrVector4(precision);
             yield return new FromYCbCrBasic(precision);
         }
 
@@ -120,7 +124,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// </summary>
         private static IEnumerable<JpegColorConverter> GetYccKConverters(int precision)
         {
+#if SUPPORTS_RUNTIME_INTRINSICS
             yield return new FromYccKAvx2(precision);
+#endif
             yield return new FromYccKVector8(precision);
             yield return new FromYccKBasic(precision);
         }
@@ -130,7 +136,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// </summary>
         private static IEnumerable<JpegColorConverter> GetCmykConverters(int precision)
         {
+#if SUPPORTS_RUNTIME_INTRINSICS
             yield return new FromCmykAvx2(precision);
+#endif
             yield return new FromCmykVector8(precision);
             yield return new FromCmykBasic(precision);
         }
@@ -140,7 +148,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
         /// </summary>
         private static IEnumerable<JpegColorConverter> GetGrayScaleConverters(int precision)
         {
+#if SUPPORTS_RUNTIME_INTRINSICS
             yield return new FromGrayscaleAvx2(precision);
+#endif
             yield return new FromGrayscaleBasic(precision);
         }
 

tests/ImageSharp.Benchmarks/Codecs/Jpeg/YCbCrColorConversion.cs

@@ -28,7 +28,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs.Jpeg
         {
             var values = new JpegColorConverter.ComponentValues(this.input, 0);
 
-            new JpegColorConverter.FromYCbCrVector(8).ConvertToRgba(values, this.output);
+            new JpegColorConverter.FromYCbCrVector4(8).ConvertToRgba(values, this.output);
         }
 
         [Benchmark]

tests/ImageSharp.Tests/Formats/Jpg/JpegColorConverterTests.cs

@@ -54,10 +54,16 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
         [Theory]
         [MemberData(nameof(CommonConversionData))]
-        public void FromYCbCrVector(int inputBufferLength, int resultBufferLength, int seed)
+        public void FromYCbCrVector4(int inputBufferLength, int resultBufferLength, int seed)
         {
+            if (!SimdUtils.HasVector4)
+            {
+                this.Output.WriteLine("No SSE present, skipping test!");
+                return;
+            }
+
             ValidateConversion(
-                new JpegColorConverter.FromYCbCrVector(8),
+                new JpegColorConverter.FromYCbCrVector4(8),
                 3,
                 inputBufferLength,
                 resultBufferLength,
@@ -346,7 +352,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             JpegColorConverter.ComponentValues values = CreateRandomValues(3, count, 1);
             var result = new Vector4[count];
 
-            JpegColorConverter converter = simd ? (JpegColorConverter)new JpegColorConverter.FromYCbCrVector(8) : new JpegColorConverter.FromYCbCrBasic(8);
+            JpegColorConverter converter = simd ? (JpegColorConverter)new JpegColorConverter.FromYCbCrVector4(8) : new JpegColorConverter.FromYCbCrBasic(8);
 
             // Warm up:
             converter.ConvertToRgba(values, result);