Re: A82: i gots a kwestun 4 yous people
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Re: A82: i gots a kwestun 4 yous people
On Mon, 2 Mar 1998, Barubary wrote:
>
> >is there any way to detect a register overflow (like "jr o, label") with
> >the z80? it could really help if there was an instruction... else, is
> >there a simple routine i can use?
>
> If you are adding, the flag you are looking for is Carry. All adds on a
> Z80 are 17 bits long (or 9 if you're doing an 8 bit add). Carry is the
> highest bit.
>
> Let's consider adding FFFF + FFFF, a combination bound to overflow.
>
> 1111 1111 1111 1111
> + 1111 1111 1111 1111
> -----------------------
> 1 1111 1111 1111 1110
> ^ ^-----------------^
> | destination reg
> carry flag
>
> The one is "carried" past the destination, so it represents overflow.
> For an add, the instruction you want is "jr c, label".
>
> -- Barubary
>
thanx... i just needed it for a favor to a friend...
i know it's a little bit late to ask, but is it ok if i add in a high
score table of sorts to Fast Tunnel for personal usage? My friends like
to compete in it, trying to get a high score, and that's the only way to
verify the score (good thing they don't know how to use a hexeditor!)...
they (and me) sometimes overflow the score, and we end up getting a really
crappy one instead. I wanted to see if i could detect that overflow, and
display how many times it did so. (no, i don't need a routine, thank
you.)
anyway, thanx again.
-Greg
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