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Re: OT : Approximate / fast math libraries ?


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


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 

Taking an example from another thread, one place I'm trying to understand is 
where I use atan2 see 


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


( note though its full of internal classes etc...)

cheers Chris

> I modified the parsing routines it used, not the floating point.
> Mike
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