Hi, On Friday 31 August 2007 8:48:49 pm Globe Trotter wrote: > Btw, I usually use -O3 rather than -O2. I agree with the other poster: I am > not sure getting rid of precision is a great idea. I don't have overall control, so cannot just switch to -03 myself. I did try it out though and it didn't make a lot of difference. Maybe I should investigate that a little deeper though to make sure something wasn't wrong. Also, I agree with you in general on the precision, just in one particular case I know I need much less than I am currently getting, and using atan2 seems to be taking significant cpu (w.r.t. the rest of the method, i.e. 50% or so). Chris > > Trotter > > ----- Original Message ---- > From: Chris Jones <jonesc@xxxxxxxxxxxxxxxxx> > To: For users of Fedora <fedora-list@xxxxxxxxxx> > Sent: Friday, August 31, 2007 2:41:56 PM > Subject: Re: OT : Approximate / fast math libraries ? > > Hi, > > Thanks for your feedback. > > > What exactly is your need? Contact me off-list and maybe I can > > help. Have you profiled your code? I have found that people > > often do not actually know where their code is spending its > > time. I once sped up an app which was universally acknowledged > > to be slow "because it uses floating point." I sped it up 3x. > > Yes, I have profiled the code, quite extensively, using the > valgrind/calltree application. From this I know this that I'm know I've > tidying up this to the point where its hard to find big improvements, the > cpu time is fairly well spread around, not isolated in a few places. So am > now looking a a few places where math calls are taking more time than I > would hope. I'm not going to get factors in speed in the overall > application, but I hope in a few places things can be improvemed a lot > locally. > > Also, the project is not small, massive in fact, and I'm only writting one > small part. If you are interested you can find it here > > http://lhcb-release-area.web.cern.ch/LHCb-release-area/DOC/brunel/releases/ >latest/doxygen/index.html > > It also has to be supported on a *lot* of hardware. Basically gcc 3.2.3 > based Scientific Linux 3 machines, gcc 3.4.6 SL4 machines (32 and 64 bit) > and (not my decision), windows VC 7.1. I cannot rely on for instance SSE > math calls etc. > > Taking an example from another thread, one place I'm trying to understand > is where I use atan2 see > > http://www.hep.phy.cam.ac.uk/~jonesc/atan2.png > > for the profiler output. atan2 is taking 50% of the time of this method. > Not here I don't need that much precision on the result - say +- > O(2*pi/100). Anything you can suggest here - The code is here > > http://www.hep.phy.cam.ac.uk/~jonesc/RichPhotonRecoUsingCKEstiFromRadius.cp >p > > ( note though its full of internal classes etc...) > > cheers Chris > > > I modified the parsing routines it used, not the floating point. > > > > Mike > > -- > > p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);} > > Oppose globalization and One World Governments like the UN. > > This message made from 100% recycled bits. > > You have found the bank of Larn. > > I can explain it for you, but I can't understand it for you. > > I speak only for myself, and I am unanimous in that! > > -- > fedora-list mailing list > fedora-list@xxxxxxxxxx > To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list > > > > > > > ___________________________________________________________________________ >_________ Pinpoint customers who are looking for what you sell. > http://searchmarketing.yahoo.com/
