Re: [boost] Compile-time power of a run-time base

From: Bruno Lalande (bruno.lalande_at_[hidden])
Date: 2008-02-17 12:04:20

Hello,

Here is a new version of the pow.hpp file with updated tests and docs. It
nows handles errors using the Boost.Math overflow error policy, and uses
promote_args to determine the return type.

I've tested it on the same platforms as before, BUT it no longer compiles
with gcc-2.95.4. The first reason was that policy.hpp includes <limits> that
gcc 2.95 doesn't have so I replaced it by <boost/limits.hpp> and it worked,
but some other Boost files include other headers that are also missing (ios
for instance, included in lcast_precision.hpp). Is the support for that
compiler required?

Bruno

On Feb 15, 2008 10:49 AM, Bruno Lalande <bruno.lalande_at_[hidden]> wrote:

> Hello,
>
> > "These rules are chosen to be compatible with the behaviour of
> > > ISO/IEC 9899:1999 Programming languages - C and with the Draft
> > > Technical Report on C++ Library Extensions, 2005-06-24, section
> > > 5.2.1, paragraph 5.
> > >
> > > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf
> > > "
> >
> > Right the idea is to be compatible with what C99 and C++0x do when an
> > integer argument is passed to a math function.
> >
>
> OK I have read this section of the draft and now I understand better the
> purpose of promote_args, so I will use it in order to to be C99 and C++0x
> compliant.
>
> > The other issue is that if:
> >
> > pow<-3>(2)
> >
> > returned an integer, then presumably it can only return 0, which isn't
> > exactly right :-)
>
> Just to see if it was even possible, I've implemented what I had talked
> about before. It takes this issue into account. Basically, here is the
> output of my test program with the result of pow on several types and their
> corresponding typeids:
> pow<2>(2) =     (i)4
> pow<2>(2.0) =   (d)4
> pow<2>(2.0f) =  (f)4
> pow<-2>(2) =    (d)0.25
> pow<-2>(2.0) =  (d)0.25
> pow<-2>(2.0f) = (d)0.25
> And regarding the way in which I did it, I "guess" a use with Boost.Unitswould give the expected result. Something like:
> pow<3>((length)5) = (volume)125;
>
>
> But the most important is to implement the promote_args version. I will
> provide this soon. After that we can always propose, as Paul said, a special
> version with a different name.
>
>
> Regards
> Bruno
>