A range of 0 to (2^36)-2 implies that there's one bit combination not mentioned here (that range has only 2 ^ 36 - 1 values; 36 bits can store 2 ^ 36). What's the last combination used for?
I don't know off-hand. AFAIU the Unisys machines use ones' complement representation. My guess is that the native unsigned set of values includes the representation for both positive and negative 0. Or there could be a trap representation that is hidden in unsigned mode, which presumably would also make these machines examples of hardware that traps on signed overflow.
