Re: [Boost-users] [mpl] compile time integer power

On 1/22/07, Sami wrote:

Hi Tony,

Thx for your reply first of all.

On 1/22/07, Gottlob Frege wrote:

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On 1/22/07, Sami wrote:

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Hi All,

if (Pow == 0) return 1; // to do argue about the value of '0 to the 0'. if (Pow == 1) return r; return pow(r) * r;

}

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Now, why do you want it - I doubt that it will buy you anything in terms of performance. The issue is not particularly about performance, it is about being able to do this at compile time; other than, well, trying out MPL. Your resolution to the problem is quite nice, though that's not what I am asking. My question is about MPL, not "how to do this with C++"...

There should be a way of doing this using MPL with a single line of code. Or, even compute integer power of integers and get a compile time result. This is useful for many metaprograms and again, not a performance concern.

Any ideas?

One more note. In my original post, I mentioned this constant sequence wrapper. If there were such a thing (is there?) then one could evaluate integer power of an integer at compile time. For instance: const unsigned SIZE = 3; const unsigned EIGHT = fold ( constant_sequence< int_<2>, SIZE >, int_<1>, times< _ , _ > :: type :: value ; This is only a thought. Maybe there is a better way of computing powers, without using fold or that constant_sequence thingy.. As for the real powers, maybe there is a Boost.Fusion algorithm that can do it.. sami.