Convert Point to Distance along 3-Dimensional Hilbert Curve?

Question

I am trying to write a function that calculates the distance along a point appears along a 3-Dimensional Hilbert Curve. Essentially a function that can take in the x, y, z coordinates of a point and calculate where on the curve it appears. Assume x, y, and z can be integers 0 - 255, roughly corresponding to the RGB colorspace. This way I can create an ordered list of points based on the Hilbert Curve.

I have tried implementing code given here on stack overflow, however this gets me stuck in a recursive loop when I try to write it in C#, furthermore isn't quite what I am after. I have also tried implementing this code, however, I must misunderstand it, because it gives me what appears to be entirely randomized results.

Currently, I am following this guide, and have gotten through coding up the section when it comes to grey-code. However, I am stuck when it comes to the example calculation with rotation. In the table, I am not sure how the final number is being produced between the chnk, rotation, and flipbit.

I am a computer science student with not much of a mathematical background.

Below is the code sample I have so far

    //This might be a little more than graycode??
    public long GreyCode()
    {
        //convert the integers in the point to a binary representation of them
        string bx = Convert.ToString(Convert.ToInt32(x), 2).PadLeft(16, '0');
        string by = Convert.ToString(Convert.ToInt32(y), 2).PadLeft(16, '0');
        string bz = Convert.ToString(Convert.ToInt32(z), 2).PadLeft(16, '0');

        //store the binary values in an array to iterate over
        int[] bxArr = bx.Select(c => c - '0').ToArray();
        int[] byArr = by.Select(c => c - '0').ToArray();
        int[] bzArr = bz.Select(c => c - '0').ToArray();

        //call a function that will iterate over each one xoring every bit together
        //Xor's each bit by it's neighboring bit to the right 
        //until it reaches the end of the array
        bxArr = XorArray(bxArr);
        byArr = XorArray(byArr);
        bzArr = XorArray(bzArr);

        //This is a magic number and I don't understand it tbh
        int rank = 4;

        //Using rank, combine the arrays and flip every rankth bit
        int[] combined = (bxArr.Concat(byArr).ToArray()).Concat(bzArr).ToArray();
        int[] bitArr = FlipBits(rank, combined);

        //rotations and stuff

        //finally, convert to integer and store
        string resStr = string.Join("", bitArr);
        long ret = Convert.ToInt64(resStr, 2);

        return ret;
    }