In article ,
Robatoy wrote:
On Apr 14, 4:30*pm, " wrote:
On Apr 14, 3:21*pm, Robatoy wrote:





On Apr 14, 11:46*am, " wrote:

On Apr 14, 8:56*am, Robatoy wrote:

On Apr 14, 9:36*am, " wrote:

On Apr 13, 4:40*pm, (Robert Bonomi) wrote:

In article
,

wrote:
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.

Really? *I've -never- seen an IC chip that did subtraction
directly. *'Adder'
chips, however, are common as dirt.

Really. *Really? You haven't looked very
hard.http://www.onsemi.com/pub_link/Colla...MC10H180-D.PDF

You can -accomplish- subtraction using an 'adder' and a
bunch of inverters
on the second input (and ignore the overflow).

True 'subtract' logic _is_ more complicated -- because the
states in the
operation table do not collapse as well.
*Addition: * *operand1 *OR operand2 == 0 *= zero result, zero carry
* * * * * * * operand1 XOR operand2 == 1 *= one *result, zero carry
* * * * * * * operand1 AND operand2 == 1 *=? zero result, one *carry

*Subtraction: operand1 *EQ operand2 * * * * * *= zero
result, zero borrow
* * * * * * * operand1 *EQ 1 AND operand2 EQ 0 = one
*result, zero borrow
* * * * * * * operand1 *EQ 0 AND operand2 EQ 1 = one
*result, one *borrow

...which are the same operations.

To expound on the 'difference' between addition and
subtraction, consider
hardware that uses "ONES COMPLEMENT" arithmetic. *Where the
'negative' of
a number is represented by simply inverting all the bits of
the positive
value. *e.g. the negative of "00000010" is "11111101".

So what? *Are you trying to prove your prowess with useless
information?

Are you showing off that the information is useless to YOU because
your prowess is so elevated?

Idiot. *A particular method of encoding negative numbers isn't
relevant when discussing the difference/similarity between subtraction
and addition. * *I wouldn't expect you to know anything about it.
OTOH, you are up to your usual standards in cashing checks with your
mouth that you ass can't cover.

Yup, you're one of 'them' alright. You ain't much.

What a moron, Robo****, but I already knew that.

Yup, you're right to the core. I find it interesting that the bulk of
your comments are degrading and condescending to justabout anybody
here. You must really think you're something. Welll... I'm here to
tell you that you are not nice.

I would have to concede Keith's expertise on the subject of morons.
*NOBODY* has the degree of _first-hand_ experience on the matter that
he does.