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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
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?

> 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...


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