Add Arm for MultiplyToAverage

Author: stefannikolei

src/ImageSharp/Formats/Jpeg/Components/Encoder/ComponentProcessor.cs

@@ -5,6 +5,7 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
 using System.Runtime.Intrinsics.X86;
 using SixLabors.ImageSharp.Memory;
 
@@ -201,12 +202,24 @@ static void MultiplyToAverage(Span<float> target, float multiplier)
 
                 // Spans are guaranteed to be multiple of 8 so no extra 'remainder' steps are needed
                 nuint count = target.Vector256Count<float>();
-                var multiplierVector = Vector256.Create(multiplier);
+                Vector256<float> multiplierVector = Vector256.Create(multiplier);
                 for (nuint i = 0; i < count; i++)
                 {
                     Unsafe.Add(ref targetVectorRef, i) = Avx.Multiply(Unsafe.Add(ref targetVectorRef, i), multiplierVector);
                 }
             }
+            else if (AdvSimd.IsSupported)
+            {
+                ref Vector128<float> targetVectorRef = ref Unsafe.As<float, Vector128<float>>(ref MemoryMarshal.GetReference(target));
+
+                // Spans are guaranteed to be multiple of 8 so no extra 'remainder' steps are needed
+                nuint count = target.Vector128Count<float>();
+                Vector128<float> multiplierVector = Vector128.Create(multiplier);
+                for (nuint i = 0; i < count; i++)
+                {
+                    Unsafe.Add(ref targetVectorRef, i) = AdvSimd.Multiply(Unsafe.Add(ref targetVectorRef, i), multiplierVector);
+                }
+            }
             else
             {
                 ref Vector<float> targetVectorRef = ref Unsafe.As<float, Vector<float>>(ref MemoryMarshal.GetReference(target));