Re: [boost] "Simple C++11 metaprogramming"

Subject: Re: [boost] "Simple C++11 metaprogramming"
From: Bruno Dutra (brunocodutra_at_[hidden])
Date: 2015-07-23 23:45:34

*<it seems I accidentally hit send, sorry about that>*

2015-07-24 0:42 GMT-03:00 Bruno Dutra <brunocodutra_at_[hidden]>:

> Peter,
>
> I can confirm peeking at the code that at least clang ships a naive linear
> recursion implementation of make_index_sequence and I read somewhere that
> GCC doesn't do any better, however it's well known
> <http://stackoverflow.com/a/17426611/801438> it may be implemented in O(log(n))
> plus taking full advantage of memoization.
> Since Part 2 of your article is all about benchmarking, have you actually
> tried it?
> I see your "duplicate immune" version of mp_contains_impl and also mp_map_find
> and hence mp_at depend on it, so I would expect one to see measurable
> improvements on their benchmarks.
> Following is an implementation if
>

Following is an implementation of it

    template<std::size_t...>

    struct indices

    {

        using type = indices;

    };

    template<typename, typename>

    struct merge_indices;

    template<std::size_t... l, std::size_t... u>

    struct merge_indices<indices<l...>, indices<u...>> :

            indices<l..., sizeof...(l) + u...>

    {};

    template<std::size_t n>

    struct make_indices;

    template<std::size_t n>

    using make_indices_t = typename make_indices<n>::type;

    template<std::size_t n>

    struct make_indices :

            merge_indices<make_indices_t<n/2>, make_indices_t<n - n/2>>

    {};

    template<>

    struct make_indices<0U> :

            indices<>

    {};

    template<>

    struct make_indices<1U> :

            indices<0U>

    {};

    template<std::size_t n>

    using make_indices_t = typename make_indices<n>::type;

Regards,
*Bruno C. O. Dutra*

>