On Apr 13, 1:33*am, Puckdropper puckdropper(at)yahoo(dot)com wrote:
" wrote :



That's not unusual at all. *Subtraction *is* adding the negative
(complement).

OTOH, the IBM 1620 was known as the CADET (Can't Add, Didn't Even
Try). *It had no ADD (or subtract) instruction at all, rather used an
index into a lookup table in memory to add. *Want a different
operator? *Overwrite the "ADD" lookup table, sometimes on purpose,
even.

In one of my CS classes, it was pointed out that ADD circuits are usually
smaller and easier than SUBtract circuits, so they're used more often. *
That's what was so weird about the subtractor being used to emulate
addition.

Not true. The (add and subtract) operations use the same logic. Now,
multiply and divide are a whole different kettle...