Challenge

Look at the following add_sub module:

  logic signed [BITS/2-1:0]       a_in;
  logic signed [BITS/2-1:0]       b_in;
  …
    {a_in, b_in} = SW;

If you were to replace a_in and b_in with a custom type that encapsulates both, would you use a structure or a union? Modify the code so that it uses your custom type, and then simulate and try it on the board.