Re: [boost] [math] pow instantiates a number of template proportional to the exponent

From: John Moeller (fishcorn_at_[hidden])
Date: 2008-05-14 22:04:27

Bruno Lalande <bruno.lalande <at> gmail.com> writes:

> 
> Hi,
> 
> > Line 54:
> >        return (N%2) ? base*positive_power<N-1>::result(base)
> >
> > in positive_power causes positive_power to be instantiated with all
> > the integers from N down to 0.
> 
> Yep you're right. At that moment I was a bit disturbed by this runtime
> evaluation but I didn't think precisely about this issue so I left it
> like that.
> 
> Adding a second integral template argument receiving N%2 to specialize
> on it works (see attachment) but I feel there's a more elegant
> solution. Maybe using enable_if?

What about:

template <int N>
struct positive_power
{
    template <typename T>
    static typename tools::promote_args<T>::type result(T base)
    {
        return ((N%2) ? base : 1) *
                       positive_power<2>::result(
                           positive_power<N/2>::result(base)
                       );
    }
};

John Moeller