What is a better way to pack 4 ints into ulong?

Question

I need to pack several int values(each value only ranging from 0 to 999) into ulong. I have a working method like below but can it be optimized?

I know it hurts your eyes with lots of 0's, sorry.

public class Test  {

    public void Start() {
        ulong testValue = 444333222111;

        Debug.Log(GetValue1(testValue) + " " + GetValue2(testValue) + " " + GetValue3(testValue) + " " + GetValue4(testValue)); // = 111 222 333 444

        SetValue1(ref testValue, 55);
        SetValue2(ref testValue, 9);
        SetValue3(ref testValue, 111);
        SetValue4(ref testValue, 999);

        Debug.Log(testValue); // = 999111009055
        Debug.Log(GetValue1(testValue) + " " + GetValue2(testValue) + " " + GetValue3(testValue) + " " + GetValue4(testValue)); // = 55 9 111 999
    }

    public int GetValue1(ulong i) => (int)(i % 1000);
    public void SetValue1(ref ulong i, int value) => i = i / 1000 * 1000 + (ulong)value;

    public int GetValue2(ulong i) => (int)(i % 1000000 / 1000);
    public void SetValue2(ref ulong i, int value) => i = i / 1000000 * 1000000 + (ulong)value * 1000 + i % 1000;

    public int GetValue3(ulong i) => (int)(i % 1000000000 / 1000000);
    public void SetValue3(ref ulong i, int value) => i = i / 1000000000 * 1000000000 + (ulong)value * 1000000 + i % 1000000;

    public int GetValue4(ulong i) => (int)(i % 1000000000000 / 1000000000);
    public void SetValue4(ref ulong i, int value) => i = i / 1000000000000 * 1000000000000 + (ulong)value * 1000000000 + i % 1000000000;

}

Answer 1

Here you go. First create a [StructLayout(LayoutKind.Explicit)] struct like:

[StructLayout(LayoutKind.Explicit)]
public struct FourWords
{
    [FieldOffset(0)] public ulong Whole;
    [FieldOffset(0)] public ushort First;
    [FieldOffset(2)] public ushort Second;
    [FieldOffset(4)] public ushort Third;
    [FieldOffset(6)] public ushort Fourth;
}

Then you can access each of the First, Second,... fields like you expect:

 FourWords test = new FourWords();
 test.Second = 0x101;
 test.Fourth = 0xA0A;
 var xyz = test.Whole;

If you look at xyz in a debugger (in hex view), you see:

    xyz, h  0x0a0a000001010000  ulong

and you can see the 101 and the A0A.