I need to find the sign of a number in C.  Maybe my reference was just
bad.  Is there an easier (less computationally intensive) way than
V/fabs(V)?


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glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:

> I need to find the sign of a number in C.  Maybe my reference was just
> bad.  Is there an easier (less computationally intensive) way than
> V/fabs(V)?

That's a bad plan if V==0 (or 0.0).

Why not simply

#define signum(x) = (x<0?-1:1)

or an obvious variation that takes 0 into account?

~Tim
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In article <86u11l1w3v.fsf@potato.vegetable.org.uk>,
Tim Haynes  <news-reply{at}stirfried.vegetable.org.uk> wrote:
>glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
> 
>
>That's a bad plan if V==0 (or 0.0).
>
>Why not simply
>
>    #define signum(x) = (x<0?-1:1)
>
>or an obvious variation that takes 0 into account?

Mainly because I usually don't use that construct, so it didn't occur to
me.  I suppose some sort of if-then is needed, then.


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furnish a nominative case to the verb 'to undulate'."
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"Gregory L. Hansen" wrote:

> I need to find the sign of a number in C.  Maybe my reference was just
> bad.  Is there an easier (less computationally intensive) way than
> V/fabs(V)?

#define sgn(x) ((x) > 0 ? +1 : (x) < 0 ? -1 : 0)

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In article <4036B2B8.302F3738@alcyone.com>,
Erik Max Francis  <max@alcyone.com> wrote:
>"Gregory L. Hansen" wrote:
> 
>
>#define sgn(x) ((x) > 0 ? +1 : (x) < 0 ? -1 : 0)

For some reason, the ()?x:y construct has always made me nervous, I'd
never used it to do anything real, and it didn't occur to me at all.  But
it seems to work.  I only needed it once, so I skipped the #define part.
But I felt sure that a function like that would have been included in the
math library.

--
"When the fool walks through the street, in his lack of understanding he
calls everything foolish." -- Ecclesiastes 10:3, New American Bible

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