using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Explicit)]
struct ByteToUlongConverter
{
    [FieldOffset(0)]
    public byte[] bytes;

    [FieldOffset(0)]
    public ulong[] ulongs;

    public ByteToUlongConverter(byte[] bytes)
    {
        this.ulongs = null;
        this.bytes = bytes;
    }
}

public class Test
{
	public static void Main()
	{
		byte[] bytes = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8 };
		ByteToUlongConverter conv = new ByteToUlongConverter(bytes);

		foreach (ulong ul in conv.ulongs)
		    Console.WriteLine($"{ul:X16}");
	}
}