Reduce JPEG color conversion to two pipelines

Author: JimBobSquarePants

src/ImageSharp/Common/Helpers/SimdUtils.cs

@@ -1,10 +1,9 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
 
@@ -36,30 +35,37 @@ internal static Vector4 PseudoRound(this Vector4 v)
 
     /// <summary>
     /// Rounds all values in 'v' to the nearest integer following <see cref="MidpointRounding.ToEven"/> semantics.
-    /// Source:
-    /// <see>
-    ///     <cref>https://github.com/g-truc/glm/blob/master/glm/simd/common.h#L110</cref>
-    /// </see>
     /// </summary>
     /// <param name="v">The vector</param>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     internal static Vector<float> FastRound(this Vector<float> v)
     {
-        if (Avx2.IsSupported)
+        if (Avx512F.IsSupported && Vector<float>.Count == Vector512<float>.Count)
+        {
+            ref Vector512<float> v512 = ref Unsafe.As<Vector<float>, Vector512<float>>(ref v);
+
+            // imm8 = 0b1000:
+            //   imm8[7:4] = 0b0000 -> preserve 0 fractional bits (round to whole numbers)
+            //   imm8[3:0] = 0b1000 -> _MM_FROUND_TO_NEAREST_INT | _MM_FROUND_NO_EXC (round to nearest even, suppress exceptions)
+            Vector512<float> vRound = Avx512F.RoundScale(v512, 0b0000_1000);
+            return Unsafe.As<Vector512<float>, Vector<float>>(ref vRound);
+        }
+
+        if (Avx2.IsSupported && Vector<float>.Count == Vector256<float>.Count)
         {
             ref Vector256<float> v256 = ref Unsafe.As<Vector<float>, Vector256<float>>(ref v);
             Vector256<float> vRound = Avx.RoundToNearestInteger(v256);
             return Unsafe.As<Vector256<float>, Vector<float>>(ref vRound);
         }
-        else
-        {
-            var magic0 = new Vector<int>(int.MinValue); // 0x80000000
-            var sgn0 = Vector.AsVectorSingle(magic0);
-            var and0 = Vector.BitwiseAnd(sgn0, v);
-            var or0 = Vector.BitwiseOr(and0, new Vector<float>(8388608.0f));
-            var add0 = Vector.Add(v, or0);
-            return Vector.Subtract(add0, or0);
-        }
+
+        // https://github.com/g-truc/glm/blob/master/glm/simd/common.h#L11
+        Vector<int> magic0 = new(int.MinValue); // 0x80000000
+        Vector<float> sgn0 = Vector.AsVectorSingle(magic0);
+        Vector<float> and0 = Vector.BitwiseAnd(sgn0, v);
+        Vector<float> or0 = Vector.BitwiseOr(and0, new Vector<float>(8388608.0f));
+        Vector<float> add0 = Vector.Add(v, or0);
+
+        return Vector.Subtract(add0, or0);
     }
 
     [Conditional("DEBUG")]

src/ImageSharp/Formats/Jpeg/Components/ColorConverters/JpegColorConverter.CmykArm64.cs

@@ -13,7 +13,7 @@ public CmykScalar(int precision)
         }
 
         /// <inheritdoc/>
-        public override void ConvertToRgbInplace(in ComponentValues values) =>
+        public override void ConvertToRgbInPlace(in ComponentValues values) =>
             ConvertToRgbInplace(values, this.MaximumValue);
 
         /// <inheritdoc/>