Hi,
after having read some comments about loop optimization somewhere, I ran
some very simple minded tests with JS for loops just loading the code
directly from the file system and found on a Lenovo X60 with Ubuntu Jaunty:
var d = [];
d[50000000]=50000000;
for (i=0; i<d.length); i++) {} // A
len = d.length; for (i=0; i<d.length); i++) {} // B
- B is more than 15% faster with FF3.5.3 and about 20% faster with Chrome
4.0.213.0 (Ubuntu build 26919)
- Firefox 3.5.3 is about 3.5 times faster than Chrome
- while and do/while loops are significantly faster than for loops in
Chrome, but slower in FF.
As the current SVN trunk of Qooxdoo has 877 type A loop statements in
framework/source/class/qx/ I thought it might be worthwhile to change these
loops from
for (i=0; i<d.length); i++) {}
to
for (i=0, len=d.length; i<len); i++) {}
where the array length doesn't change within the for loop.
Thinking a bit further I figured that the performance gain might be marginal
for any significant amount of code inside the loop. And indeed, adding just
the simple line
r = n*33;
inside the loop made the difference in the for loops disappear, even for n=0
...
So, I guess, measuring when trying to optimize for performance makes a lot
of sense ... and just optimizing the control structure of a look doesn't
gain that much. So the code inside the loop is where to search for
improvements.
Not really a very deep insight, but I thought I want to share this with you
anyway, as these kinds of "urban coding myth" come up every once in a while.
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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