Optimizing C code

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.}