Re: [boost] mcs::units informal review request

From: Matthias Schabel (boost_at_[hidden])
Date: 2007-01-28 15:05:36

> Ok, I probably won't get to do this until Friday again...that's the  
> day
> I get to work on personal things at work for a few hours...I don't  
> have VC.

I don't have access to it at all, so I appreciate any help in getting  
things to function
correctly under VC++...

> I was profiling my own version and it was dog slow compared to  
> doubles.
>  I wanted to check yours.  I did here at home with g++ on Linux and  
> our
> two versions compare equally wrt the static dim quantity.  I had to
> really vamp up the optimizations of course to get them as fast as
> doubles (I couldn't find the right options for VC) and I still  
> can't do

I haven't spent much time (following the Boost admonition to focus on
clarity and correctness before optimization) tuning performance yet.  
I don't believe
that there is anything in the quantity class that can't, in  
principle, be optimized
away. That being said, principle and practice can be separated by a  
significant
gulf at times...good compiler inlining will be critical to optimization.

Any input on optimizing the library would be most welcome - I expect  
that it should
be possible to have code using quantities run exactly as fast as for  
built in types,
but that remains to be proven...

> as deep a recursion level without a seg fault...this is actually by
> quite a margin...several orders of magnitude.  Both versions fail  
> at the
> same point.  Here is test code...add a 0 to the end of tlim and I  
> get a
> crash on the quantity version:

I'm personally more concerned about runtime performance than  
recursion at this
point, but this is an interesting point... I'm not completely clear  
on what you mean
about increasing tlim : do you mean that the equivalent code with  
doubles can
recurse several orders of magnitude deeper, and mcs::units recurses  
one order
of magnitude deeper than your quantity code?

> COMMAND LINE:
>
> nroberts_at_localhost ~/projects/prof_units $ g++ -I/home/nroberts/units
> -pg -O3 prof_mcs.cpp
>
> This is likely implementation dependant and maybe there's still  
> more ops.

It looks like I'm having a dumb day today. Do you mean that there are  
more operations
in the quantity code than there are for doubles???

Anyway, thanks for the feedback...

Matthias