On 29.09.2009 13:38, Fritz Zaucker wrote:
> 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 ...
>
>
he-he :)
> 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;
> }
>
maybe you want to put new Date()
inside loop?
> 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
>
>
--
Best Regards
Alexander Yerenkow,
Generalissimo of UCT
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