Calculate XY to D for hilbert curve (Convert C code)

I am trying to convert this bit of code from this wikipedia article from C to Delphi.

//convert (x,y) to d
int xy2d (int n, int x, int y) {
    int rx, ry, s, d=0;
    for (s=n/2; s>0; s/=2) {
        rx = (x & s) > 0;
        ry = (y & s) > 0;
        d += s * s * ((3 * rx) ^ ry);
        rot(s, &x, &y, rx, ry);
    }
    return d;
}

I cannot find an equivalent to the rot function used there

You can use the the Var keyword to pass functions by reference in Delphi, which achieves the same result as passing pointers to ints in the linked C code:

procedure Rot(N : Integer; RX, RY : Boolean; Var X, Y : Integer);
 var
   T : Integer;
 begin
   If Not RY then
   begin
     If RX then
     begin
       X := N - 1 - X;
       Y := N - 1 - Y;
     end;
       T := X;
       X := Y;
       Y := T;
   end;
 end;

Note that the parameter order has changed. I grouped the parameters passed by reference and those passed by value together. You can use Booleans instead of Integers for RX and RY (make sure you adapt the calling code appropriately though).