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Forums > C64 Coding > How is carry affected by compare?
2010-11-10 19:40
Mace

Registered: May 2002
Posts: 1799
How is carry affected by compare?

Somewhere I read that the carry is affected by the result of a compare.
It's not in the Prog.Ref.Guide, other than a flag in the register table.

How does this work?
 
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2010-11-12 15:57
GT
Account closed

Registered: Sep 2008
Posts: 308
IMHO Oswald and Jackasser are confusing newbe's with "big-coca-cola-glasses", trying to explain what goes on inside the silicon.

CMP #$40 for instance, gives you the same result(READ RESULT) except touching the A, as:

SEC
SBC #$40

Don't listen to them newbe's.

;-)
2010-11-12 16:16
GT
Account closed

Registered: Sep 2008
Posts: 308
I do admire Oswald and Jackasser coding skills. Don't take me wrong. :)

I'm curious, though, about the inner workings. I guess Mace got his answer how the CMP affects the carry by now?! :)
2010-11-12 18:29
JackAsser

Registered: Jun 2002
Posts: 2014
Quote: I do admire Oswald and Jackasser coding skills. Don't take me wrong. :)

I'm curious, though, about the inner workings. I guess Mace got his answer how the CMP affects the carry by now?! :)


Mnaw! :D But yeah, we're just attention whores really! :D Happy WE!
2010-11-12 18:40
Mace

Registered: May 2002
Posts: 1799
Yes, the answer is clear. Thanks for that!
And although the related subjects are interesting too, I think most if not all is said by now ;-)
2010-11-12 20:56
Oswald

Registered: Apr 2002
Posts: 5076
what jackie said, and as I think about it, implementing it with the "implied" SEC way may be just as simple as doing an SBC which just ignores the carry. Someone ask Chuck Peddle :)
2010-11-13 09:57
GT
Account closed

Registered: Sep 2008
Posts: 308
Quote: what jackie said, and as I think about it, implementing it with the "implied" SEC way may be just as simple as doing an SBC which just ignores the carry. Someone ask Chuck Peddle :)

A simple SBC doesn't ignore the carry.
2010-11-13 10:31
Oswald

Registered: Apr 2002
Posts: 5076
I speculate about how cmp does its thing, wether it has a built in sec, or it just ignores the carry.
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