I think you are confused. Unsigned arithmetic is modular. Unsigned integers are both positive and negative. 0b1111_1111 is congruent to both -1 and 255 (mod 25

I think you are confused. Unsigned arithmetic is modular. Unsigned integers are both positive and negative. 0b1111_1111 is congruent to both -1 and 255 (mod 256). We simply choose the value 255 as being the principle value for coercions, but you could equally well choose -1. Is 3pm tomorrow or yesterday? Yes. Unsigned != non-negative.