On Tue, 29 Sep 2009, A.Yerenkow wrote:
> You could find info in internet about why is that :)
> The javascript arrays aren't arrays at all :)
> To see the whole picture, try reverse tests, like this:
>
> a) var k, n = 5000000;
> var d=[];
> for (k=n; k>0; k--) {
> d[k] = k;
> }
>
> .....
>
> d) var k, n = 5000000;
> var d=[];
> d[n]=n;
> for (k=n; k>0; k--){
> d[k] = k;
> }
>
> e) var k, n = 5000000;
>
> var d=[];
> d[0]=0;
> for (k=n; k>0; k--){
> d[k] = k;
> }
Oops ... about a factor 30-80 slower than the forward versions with FF
3.5.3, but "only" about a factor of 5 slower in Chrome ...
Good to know, especially as some loop optimisation suggestions I found
recommend looping downwards (which indeed might make the loop control
structure faster, but the actual code inside the loop dominating the picture
completely in this example).
Another "interesting" result:
n = 20000000;
var k, d=[];
for (k=0; k<n; k++) {
d[d.length]=k;
}
is basically as fast as
n = 20000000;
var d = new Array(n);
var t2= new Date().getTime();
for (k=0; k<n; k++) {
d[k] = k;
}
and about 40% faster (FF 3.5.3) and about 10% faster (Chrome) as the
push-version while doing exactly the same. Is this due to the method call
overhead of .push() or does push() do something fancy?
I don't have a very clean setup for IE-Testing, but at first glance the
effects seem similar.
Cheers,
Fritz
--
Oetiker+Partner AG tel: +41 62 775 99 03 (direct)
Fritz Zaucker +41 62 775 99 00 (switch board)
Aarweg 15 +41 79 675 06 30 (mobile)
CH-4600 Olten fax: +41 62 775 99 05
Schweiz web: www.oetiker.ch
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