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140 lines
3.1 KiB
140 lines
3.1 KiB
// Boost pow.hpp header file |
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// Computes a power with exponent known at compile-time |
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// (C) Copyright Bruno Lalande 2008. |
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// Distributed under the Boost Software License, Version 1.0. |
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// (See accompanying file LICENSE_1_0.txt or copy at |
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// http://www.boost.org/LICENSE_1_0.txt) |
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// See http://www.boost.org for updates, documentation, and revision history. |
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#ifndef BOOST_MATH_POW_HPP |
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#define BOOST_MATH_POW_HPP |
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#include <boost/math/policies/policy.hpp> |
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#include <boost/math/policies/error_handling.hpp> |
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#include <boost/math/tools/promotion.hpp> |
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#include <boost/mpl/greater_equal.hpp> |
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namespace boost { |
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namespace math { |
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namespace detail { |
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template <int N, int M = N%2> |
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struct positive_power |
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{ |
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template <typename T> |
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static T result(T base) |
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{ |
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T power = positive_power<N/2>::result(base); |
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return power * power; |
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} |
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}; |
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template <int N> |
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struct positive_power<N, 1> |
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{ |
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template <typename T> |
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static T result(T base) |
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{ |
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T power = positive_power<N/2>::result(base); |
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return base * power * power; |
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} |
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}; |
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template <> |
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struct positive_power<1, 1> |
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{ |
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template <typename T> |
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static T result(T base){ return base; } |
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}; |
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template <int N, bool> |
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struct power_if_positive |
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{ |
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template <typename T, class Policy> |
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static T result(T base, const Policy&) |
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{ return positive_power<N>::result(base); } |
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}; |
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template <int N> |
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struct power_if_positive<N, false> |
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{ |
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template <typename T, class Policy> |
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static T result(T base, const Policy& policy) |
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{ |
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if (base == 0) |
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{ |
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return policies::raise_overflow_error<T>( |
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"boost::math::pow(%1%)", |
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"Attempted to compute a negative power of 0", |
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policy |
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); |
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} |
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return T(1) / positive_power<-N>::result(base); |
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} |
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}; |
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template <> |
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struct power_if_positive<0, true> |
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{ |
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template <typename T, class Policy> |
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static T result(T base, const Policy& policy) |
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{ |
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if (base == 0) |
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{ |
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return policies::raise_indeterminate_result_error<T>( |
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"boost::math::pow(%1%)", |
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"The result of pow<0>(%1%) is undetermined", |
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base, |
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T(1), |
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policy |
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); |
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} |
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return T(1); |
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} |
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}; |
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template <int N> |
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struct select_power_if_positive |
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{ |
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typedef typename mpl::greater_equal< |
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mpl::int_<N>, |
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mpl::int_<0> |
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>::type is_positive; |
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typedef power_if_positive<N, is_positive::value> type; |
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}; |
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} // namespace detail |
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template <int N, typename T, class Policy> |
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inline typename tools::promote_args<T>::type pow(T base, const Policy& policy) |
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{ |
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typedef typename tools::promote_args<T>::type result_type; |
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return detail::select_power_if_positive<N>::type::result(static_cast<result_type>(base), policy); |
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} |
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template <int N, typename T> |
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inline typename tools::promote_args<T>::type pow(T base) |
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{ return pow<N>(base, policies::policy<>()); } |
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} // namespace math |
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} // namespace boost |
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#endif
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