Keith Burzinski <tsk3000@Prodigy.Net> wrote:

> What's the quickest way to check if a number is negative?  Can I
> just test bit 7?

    Yes.

> I just tried subtracting 0 from the register using 'subwf', but
> that seems to _always_ leave the C flag set.

    Of course it does; SUBWF treats the two numbers as UNSIGNED
    (i.e., non-negative), so subtracting 0 always gives (as far as
    SUBWF is concerned) a non-negative result.

> And if I add 0 using 'addwf', it always leaves the C flag clear.

    This happens because the ADDWF instruction only sets the carry
    flag if the result is greater than 255, and adding 0 to an 8-bit
    number can NEVER result in an answer that's greater than 255.

> Will just tesing bit 7 of the reg always work?

    Yes.

    -Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
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