Hi, On Tue, 2009-06-02 at 16:56 -0400, Christopher Montgomery wrote: > > As far as I know pretty much any compiler out there should be able to > > replace a modulo by a power-of-2 constant by the bit-wise AND operation > > without us explicitly doing so (see also > > http://en.wikipedia.org/wiki/Modulo_operation#Performance_issues). So > > for the benefit of readable code I suggest that we keep the code as it > > is. > > Interesting. I got a noticable and repeatable performance benefit. > Which is not to say I haven't somehow mismeasured it. I agree the > modulo is more readable. > > ...perhaps the difference is the difference of (x) or (y) possibly > being negative and additional conformance-related assembly getting > generated? I suppose there's no reason to speculate, I'll go read the > assembly gcc generates and that will answer everything, at least for > me. I might very well be wrong here. If there's indeed a difference in the generated assembly and a noticeable performance benefit, than let's use the optimized macro. But perhaps we can add a short comment there explaining that ((y) & (TILE_HEIGHT-1)) is equivalent to ((y) % TILE_HEIGHT). Not everyone reading this code will be aware of this immediately. Sven _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
