boost/hana/power.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::power`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_POWER_HPP
0011 #define BOOST_HANA_POWER_HPP
0012
0013 #include <boost/hana/fwd/power.hpp>
0014
0015 #include <boost/hana/concept/integral_constant.hpp>
0016 #include <boost/hana/concept/ring.hpp>
0017 #include <boost/hana/config.hpp>
0018 #include <boost/hana/core/dispatch.hpp>
0019 #include <boost/hana/functional/iterate.hpp>
0020 #include <boost/hana/functional/partial.hpp>
0021 #include <boost/hana/mult.hpp>
0022 #include <boost/hana/one.hpp>
0023
0024 #include <cstddef>
0025
0026
0027 namespace boost { namespace hana {
0028     //! @cond
0029     template <typename X, typename N>
0030     constexpr decltype(auto) power_t::operator()(X&& x, N const& n) const {
0031         using R = typename hana::tag_of<X>::type;
0032         using Power = BOOST_HANA_DISPATCH_IF(power_impl<R>,
0033             hana::Ring<R>::value &&
0034             hana::IntegralConstant<N>::value
0035         );
0036
0037     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0038         static_assert(hana::Ring<R>::value,
0039         "hana::power(x, n) requires 'x' to be in a Ring");
0040
0041         static_assert(hana::IntegralConstant<N>::value,
0042         "hana::power(x, n) requires 'n' to be an IntegralConstant");
0043     #endif
0044
0045         static_assert(N::value >= 0,
0046         "hana::power(x, n) requires 'n' to be non-negative");
0047
0048         return Power::apply(static_cast<X&&>(x), n);
0049     }
0050     //! @endcond
0051
0052     template <typename R, bool condition>
0053     struct power_impl<R, when<condition>> : default_ {
0054         template <typename X, typename N>
0055         static constexpr decltype(auto) apply(X&& x, N const&) {
0056             constexpr std::size_t n = N::value;
0057             return hana::iterate<n>(
0058                 hana::partial(hana::mult, static_cast<X&&>(x)),
0059                 hana::one<R>()
0060             );
0061         }
0062     };
0063 }} // end namespace boost::hana
0064
0065 #endif // !BOOST_HANA_POWER_HPP