Message-ID: <4B59F01C.4070802@stats.uwo.ca>
Date: 2010-01-22T18:36:12Z
From: Duncan Murdoch
Subject: Optimizing C code
In-Reply-To: <4B59E5C8.2050203@u-paris10.fr>
On 22/01/2010 12:52 PM, Christophe Genolini wrote:
> Thanks both of you.
>
> >
> > > Inf - Inf
> > [1] NaN
> So isn't the line 9 useless ? If either x[i] or y[i] are NA, then dev
> will be NA and !ISNAN(dev) will detect it...
> Sothe loop cool be
>
> 8. for(i = 0 ; i < taille ; i++) {
> 10. dev = (x[i] - y[i]);
> 11. if(!ISNAN(dev)) {
> 12. dist += dev * dev;
> 13. count++;
> 15. }
> 16. }
>
> No ?
>
That would presumably give the same answer, but there are lots of
reasons it might not be useless:
- the author might find it clearer, or easier to generalize to integer
data (where your version wouldn't work).
- it might be faster, because it can abort sooner.
- it might be essentially equivalent in all important respects.
Duncan Murdoch
> Christophe
> > Duncan Murdoch
> >> Christophe
> >>
> >>
> >> #define both_FINITE(a,b) (R_FINITE(a) && R_FINITE(b))
> >> #define both_non_NA(a,b) (!ISNAN(a) && !ISNAN(b))
> >>
> >> 1. static double R_euclidean2(double *x, double *y, int taille)
> >> 2. {
> >> 3. double dev, dist;
> >> 4. int count, i;
> >> 5.
> >> 6. count= 0;
> >> 7. dist = 0;
> >> 8. for(i = 0 ; i < taille ; i++) {
> >> 9. if(both_non_NA(x[i], y[i])) {
> >> 10. dev = (x[i] - y[i]);
> >> 11. if(!ISNAN(dev)) {
> >> 12. dist += dev * dev;
> >> 13. count++;
> >> 14. }
> >> 15. }
> >> 16. }
> >> 17. if(count == 0)return NA_REAL;
> >> 18. if(count != taille) dist /= ((double)count/taille);
> >> 19. return sqrt(dist);
> >> 20.}
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> >
>