Am Tue, 15 Jun 2010 09:18:45 +0200
schrieb Jan Holst Jensen <j...@biochemfusion.com>:
> On 2010-06-15 09:06, Bartosz wrote:
> > By the way.
> > After replace svArrays by STL containers, in some cases I observed
> > boost of performance.
> >
> > For example:
> > for (USHORT i = 0; i< aEntries.size(); ++i)
> > {
> >
> > if (aEntries.at(i).aFntFmt == rFntFmt)
> > {
> > aRes = aEntries[i].aId;
> > break;
> > }
> > }
> >
> > is much faster than:
> >
> > USHORT nCnt = aEntries.Count();
> > USHORT i;
> > for (i = 0; i< nCnt&& 0 == aRes.Len(); ++i)
> > {
> > if (aEntries[i].aFntFmt == rFntFmt)
> > aRes = aEntries[i].aId;
> > }
> >
>
> If you're about to optimize then try the iterator-version of above as
> well. Something like (not tested, off the top of my head, and I don't
> know the actual type of aEntries):
>
> EntryType::iterator end = aEntries.end();
> for (EntryType::iterator i = aEntries.begin(); i != end; i++)
> {
>
> if (i->aFntFmt == rFntFmt)
> {
> aRes = i->aId;
> break;
> }
> }
>
> In some of the code that I work on (not OOo, but another C++ project)
> I have seen a very nice performance boost by switching from
> array-style subscripting to iterators.
Having measured performance on container access ad nauseum for
new_itemsets I can only warn you about such generic statements: For
example the new_itemsets cws seems to be 2-8% faster for loading and
saving on unix, while seeming to be ~8% slower on loading on windows
currently. So while measuring with callgrind is helping, it is only
part of the truth -- especially since it is partially synthetic. Also
measuring on a high-end i7 developer machine might be misleading,
since the scenario were we care about performance (meek netbooks etc.)
have completely different CPU-caches etc., resulting in possible
completely different performances.
Best Regards,
Bjoern
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