Re: how to decide the value of SF

Phil Carmody wrote:
Sebastian Biallas <spamtrap@xxxxxxxxxx> writes:
Phil Carmody wrote:
Sebastian Biallas <spamtrap@xxxxxxxxxx> writes:

Tim Roberts wrote:
spamtrap@xxxxxxxxxx wrote:
if sub ax,ax(two numbers compared,the resulst is neither a plus nor
a negative )
how to determine the value of SF?
0 is a positive number.
No. By the usual mathematical definition, 0 is neither positiv nor negative.
By the usual x86 definition, 0 is positive.
The SF is set iff the result is negative (i.e. the MSB is set). So if it
isn't set, all you know is that the number is non-negative. Non-negative
is not the same as positive.

I know this isn't the definition for positive, but it's relevant -
do you agree with this definition:

natural number
n. One of the set of positive whole numbers; a positive integer.

Even in mathematics there is no unique definition of natural numbers.
Some define 0 to be a natural number, for some 0 isn't one. There are
arguments for both definitions.

But the definition for positive number is pretty clear: A number > zero.

And the definition makes sense: If you negate a positiv number, you get
a negative one (and vice versa). (This has a caveat on x86 since the
positive and negative numbers are not symmetric with twos complement).

Between you and me, I'm also interested to know how many integer values
you think there are between 0 and 127? Again, it is relevant.

This pretty much depends on what "between" means (including or
excluding). But I'm not a native english speaker, maybe "between" has
clear semantics in english.

You seem to fail to realise how much convention plays a part in communication,
and that there may be different conventions in different contexts. Even 1
was prime for some great mathematicians last century.

That is correct. But I don't remeber that Intel used a different
convention in the x86 specification.

--
Gruß,
Sebastian

.

Relevant Pages

  • Re: how to decide the value of SF
    ... By the usual mathematical definition, 0 is neither positiv nor negative. ... One of the set of positive whole numbers; a positive integer. ... You seem to fail to realise how much convention plays a part in communication, ...
    (comp.lang.asm.x86)
  • Re: how to decide the value of SF
    ... Sebastian Biallas writes: ... By the usual mathematical definition, 0 is neither positiv nor negative. ... /In God We Trust, Inc./. ...
    (comp.lang.asm.x86)
  • Re: how to decide the value of SF
    ... Phil Carmody wrote: ... By the usual mathematical definition, 0 is neither positiv nor negative. ... The SF is set iff the result is negative (i.e. the MSB is set). ...
    (comp.lang.asm.x86)