[postgis-devel] strange behavoir of LW_ABS

[Mateusz Loskot]

nicklas.aven at jordogskog.no wrote:
> Maybe this is my lack of c-knowledge, but i'm very confused of
> the behavior of LW_ABS
> The code below I thought would return -1, but i returns -3.

You mean positive 1.

> Is this expected behavior?
> 
> Why do we have LW_ABS() instead of fabs() ?
> 
>
> #include <stdio.h> 
> #define LW_ABS(a)   ((a) < (0) ? (-a) : (a))
> int main() 
> {
> int d,e,f;
> d = 1;
> e = -2;
> f = LW_ABS(d+e);

Replace with:

f = LW_ABS( (d+e) );

And see if there is any difference.
Yet another example of evilness of macros ;-)

Best regards,
--
Mateusz Loskot
Senior Programmer, Cadcorp
http://www.cadcorp.com
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