Add missing Non-SIMD implementation

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.Generated.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 
@@ -96,7 +97,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         {
             Vector4 CMin4 = new Vector4(0F);
             Vector4 CMax4 = new Vector4(maximum);
-            Vector4 COff4 = new Vector4(maximum/2 + 1);
+            Vector4 COff4 = new Vector4((float)Math.Ceiling(maximum/2));
 
             this.V0L = Vector4.Clamp(this.V0L + COff4, CMin4, CMax4);
             this.V0R = Vector4.Clamp(this.V0R + COff4, CMin4, CMax4);
@@ -122,7 +123,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         [MethodImpl(InliningOptions.ShortMethod)]
         public void NormalizeColorsAndRoundInplaceAvx2(float maximum)
         {
-            Vector<float> off = new Vector<float>(maximum/2 +1);
+            Vector<float> off = new Vector<float>((float)Math.Ceiling(maximum/2));
             Vector<float> max = new Vector<float>(maximum);
             
             ref Vector<float> row0 = ref Unsafe.As<Vector4, Vector<float>>(ref this.V0L);

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.Generated.tt

@@ -11,6 +11,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 
@@ -61,7 +62,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         {
             Vector4 CMin4 = new Vector4(0F);
             Vector4 CMax4 = new Vector4(maximum);
-            Vector4 COff4 = new Vector4(maximum/2 + 1);
+            Vector4 COff4 = new Vector4((float)Math.Ceiling(maximum/2));
 
             <#
 
@@ -85,7 +86,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components
         [MethodImpl(InliningOptions.ShortMethod)]
         public void NormalizeColorsAndRoundInplaceAvx2(float maximum)
         {
-            Vector<float> off = new Vector<float>(maximum/2 +1);
+            Vector<float> off = new Vector<float>((float)Math.Ceiling(maximum/2));
             Vector<float> max = new Vector<float>(maximum);
             <#
 

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

@@ -17,10 +17,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
 
             public override void ConvertToRgba(in ComponentValues values, Span<Vector4> result)
             {
-                ConvertCore(values, result);
+                ConvertCore(values, result, this.MaximumValue, this.HalfValue);
             }
 
-            internal static void ConvertCore(in ComponentValues values, Span<Vector4> result)
+            internal static void ConvertCore(in ComponentValues values, Span<Vector4> result, float maxValue, float halfValue)
             {
                 // TODO: We can optimize a lot here with Vector<float> and SRCS.Unsafe()!
                 ReadOnlySpan<float> yVals = values.Component0;
@@ -29,13 +29,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
 
                 var v = new Vector4(0, 0, 0, 1);
 
-                var scale = new Vector4(1 / 255F, 1 / 255F, 1 / 255F, 1F);
+                var scale = new Vector4(1 / maxValue, 1 / maxValue, 1 / maxValue, 1F);
 
                 for (int i = 0; i < result.Length; i++)
                 {
                     float y = yVals[i];
-                    float cb = cbVals[i] - 128F;
-                    float cr = crVals[i] - 128F;
+                    float cb = cbVals[i] - halfValue;
+                    float cr = crVals[i] - halfValue;
 
                     v.X = MathF.Round(y + (1.402F * cr), MidpointRounding.AwayFromZero);
                     v.Y = MathF.Round(y - (0.344136F * cb) - (0.714136F * cr), MidpointRounding.AwayFromZero);

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

@@ -28,7 +28,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                     ConvertCore(values.Slice(0, simdCount), result.Slice(0, simdCount), this.MaximumValue, this.HalfValue);
                 }
 
-                FromYCbCrBasic.ConvertCore(values.Slice(simdCount, remainder), result.Slice(simdCount, remainder));
+                FromYCbCrBasic.ConvertCore(values.Slice(simdCount, remainder), result.Slice(simdCount, remainder), 
+                    this.MaximumValue, this.HalfValue);
             }
 
             /// <summary>

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromYCbCrSimdAvx2.cs

@@ -28,16 +28,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 int simdCount = result.Length - remainder;
                 if (simdCount > 0)
                 {
-                    ConvertCore(values.Slice(0, simdCount), result.Slice(0, simdCount));
+                    ConvertCore(values.Slice(0, simdCount), result.Slice(0, simdCount), 
+                        this.MaximumValue, this.HalfValue);
                 }
 
-                FromYCbCrBasic.ConvertCore(values.Slice(simdCount, remainder), result.Slice(simdCount, remainder));
+                FromYCbCrBasic.ConvertCore(values.Slice(simdCount, remainder), result.Slice(simdCount, remainder), 
+                    this.MaximumValue, this.HalfValue);;
             }
 
             /// <summary>
             /// SIMD convert using buffers of sizes divisible by 8.
             /// </summary>
-            internal static void ConvertCore(in ComponentValues values, Span<Vector4> result)
+            internal static void ConvertCore(in ComponentValues values, Span<Vector4> result, float maxValue, float halfValue)
             {
                 // This implementation is actually AVX specific.
                 // An AVX register is capable of storing 8 float-s.
@@ -57,7 +59,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 ref Vector4Octet resultBase =
                     ref Unsafe.As<Vector4, Vector4Octet>(ref MemoryMarshal.GetReference(result));
 
-                var chromaOffset = new Vector<float>(-128f);
+                var chromaOffset = new Vector<float>(-halfValue);
 
                 // Walking 8 elements at one step:
                 int n = result.Length / 8;
@@ -70,7 +72,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 ref Vector<float> ggRefAsVector = ref Unsafe.As<Vector4Pair, Vector<float>>(ref gg);
                 ref Vector<float> bbRefAsVector = ref Unsafe.As<Vector4Pair, Vector<float>>(ref bb);
 
-                var scale = new Vector<float>(1 / 255f);
+                var scale = new Vector<float>(1 / maxValue);
 
                 for (int i = 0; i < n; i++)
                 {

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

@@ -41,7 +41,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs.Jpeg
         {
             var values = new JpegColorConverter.ComponentValues(this.input, 0);
 
-            JpegColorConverter.FromYCbCrBasic.ConvertCore(values, this.output);
+            JpegColorConverter.FromYCbCrBasic.ConvertCore(values, this.output, 255F, 128F);
         }
 
         [Benchmark]
@@ -49,7 +49,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs.Jpeg
         {
             var values = new JpegColorConverter.ComponentValues(this.input, 0);
 
-            JpegColorConverter.FromYCbCrSimd.ConvertCore(values, this.output);
+            JpegColorConverter.FromYCbCrSimd.ConvertCore(values, this.output, 255F, 128F);
         }
 
         [Benchmark]
@@ -57,7 +57,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs.Jpeg
         {
             var values = new JpegColorConverter.ComponentValues(this.input, 0);
 
-            JpegColorConverter.FromYCbCrSimdAvx2.ConvertCore(values, this.output);
+            JpegColorConverter.FromYCbCrSimdAvx2.ConvertCore(values, this.output, 255F, 128F);
         }
 
         private static Buffer2D<float>[] CreateRandomValues(