Who's afraid of a big bad optimizing compiler?

I was using ones-complement systems in the 1980s, and there were ones-/two-complement debates at that time, but fair enough on your point about the introduction dates.

If I remember correctly, the usual way to do unsigned arithmetic on ones-complement-only systems was to force the sign bit clear after each addition and subtraction operation. And the ones-complement CDC 6600 systems used floating point to do integer multiplication and division, which required tricks normally used in multiple-precision arithmetic to get a 60-bit unsigned result out of floating-point operations with 48-bit mantissas. One reason that this worked was that there was a separate instruction for normalizing floating-point numbers, as well as another instruction that produced the lower 48 bits of the 96-bit product of two 48-bit mantissas.

Fun times! ;-)