Accelerate Vector128<long>::op_Multiply on x64

src/libraries/System.Private.CoreLib/src/System/Runtime/Intrinsics/Vector128_1.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
@@ -7,6 +7,8 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.Arm;
+using System.Runtime.Intrinsics.X86;
 using System.Text;
 
 namespace System.Runtime.Intrinsics
@@ -261,6 +263,29 @@ public static Vector128<T> Zero
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static Vector128<T> operator *(Vector128<T> left, Vector128<T> right)
         {
+            // TODO: move this to JIT
+            if (AdvSimd.Arm64.IsSupported && typeof(T) == typeof(ulong))
+            {
+                Vector128<ulong> a = left.AsUInt64();
+                Vector128<ulong> b = left.AsUInt64();
+                return AdvSimd.Arm64.UnzipEven(
+                    AdvSimd.MultiplyWideningLower(
+                        a.GetLower().AsUInt32(), b.GetLower().AsUInt32()).AsUInt16(),
+                    AdvSimd.MultiplyWideningUpper(
+                        a.AsUInt32(), b.AsUInt32()).AsUInt16()).AsUInt64().As<ulong, T>();
+            }
+            if (Sse41.IsSupported)
+            {
+                Vector128<ulong> a = left.AsUInt64();
+                Vector128<ulong> b = left.AsUInt64();
+                return Sse2.Add(
+                    Sse2.Multiply(a.AsUInt32(), b.AsUInt32()).AsUInt64(),
+                    Sse2.Shuffle(
+                        Ssse3.HorizontalAdd(
+                            Sse41.MultiplyLow(a.AsUInt32(),
+                                Sse2.Shuffle(b.AsUInt32(), 0xB1)).AsInt32(), Vector128<int>.Zero), 0x73).AsUInt64()).As<ulong, T>();
+            }
+
             return Vector128.Create(
                 left._lower * right._lower,
                 left._upper * right._upper