Pointer to struct containing System.Numerics.Vector<double> in C#

Question

I'm trying to make vector with 4 doubles with System.Numerics library because of SIMD. So I made this struct:

public struct Vector4D
{
    System.Numerics.Vector<double> vecXY, vecZW;

    ...

}

In this phase I code it for 128bit SIMD register. It works fine, but when I want something like this:

Vector4D* pntr = stackalloc Vector4D[8];

I get this:

Cannot take the address of, get the size of, or declare a pointer to a managed type ('Vector4D')

Any idea how to use stackalloc with System.Numerics.Vector? With System.Numerics.Vector4 (which is float-precision) there is no problem with pointers, but I need double-precision.

Answer 1

I solved it:

public struct Vector4D
{
    public double X, Y, Z, W;

    private unsafe Vector<double> vectorXY
    {
        get
        {
            fixed (Vector4D* ptr = &this)
            {
                return SharpDX.Utilities.Read<Vector<double>>((IntPtr)ptr);
            }
        }
        set
        {
            fixed (Vector4D* ptr = &this)
            {
                SharpDX.Utilities.Write<Vector<double>>((IntPtr)ptr, ref value);
            }
        }
    }

    private unsafe Vector<double> vectorZW
    {
        get
        {
            fixed (Vector4D* ptr = &this)
            {
                return SharpDX.Utilities.Read<Vector<double>>((IntPtr)((double*)ptr) + 2);
            }
        }
        set
        {
            fixed (Vector4D* ptr = &this)
            {
                SharpDX.Utilities.Write<Vector<double>>((IntPtr)((double*)ptr) + 2, ref value);
            }
        }
    }
...
}

This gives you Vector for SIMD operations and also you can use pointer to struct. Unfortunately it's around 50% slower than using static array without SIMD.