math/special_functions/pow.hpp

0001 //   Boost pow.hpp header file
0002 //   Computes a power with exponent known at compile-time
0003
0004 //  (C) Copyright Bruno Lalande 2008.
0005 //  (C) Copyright Matt Borland 2024.
0006 //  Distributed under the Boost Software License, Version 1.0.
0007 //  (See accompanying file LICENSE_1_0.txt or copy at
0008 //  http://www.boost.org/LICENSE_1_0.txt)
0009
0010 //  See http://www.boost.org for updates, documentation, and revision history.
0011
0012
0013 #ifndef BOOST_MATH_POW_HPP
0014 #define BOOST_MATH_POW_HPP
0015
0016 #include <boost/math/tools/config.hpp>
0017 #include <boost/math/policies/policy.hpp>
0018 #include <boost/math/policies/error_handling.hpp>
0019 #include <boost/math/tools/promotion.hpp>
0020
0021 #ifndef BOOST_MATH_HAS_NVRTC
0022 #include <boost/math/special_functions/math_fwd.hpp>
0023 #endif
0024
0025 namespace boost {
0026 namespace math {
0027
0028 #ifdef _MSC_VER
0029 #pragma warning(push)
0030 #pragma warning(disable:4702) // Unreachable code, only triggered in release mode and /W4
0031 #endif
0032
0033 namespace detail {
0034
0035
0036 template <int N, int M = N%2>
0037 struct positive_power
0038 {
0039     template <typename T>
0040     BOOST_MATH_GPU_ENABLED static constexpr T result(T base)
0041     {
0042         T power = positive_power<N/2>::result(base);
0043         return power * power;
0044     }
0045 };
0046
0047 template <int N>
0048 struct positive_power<N, 1>
0049 {
0050     template <typename T>
0051     BOOST_MATH_GPU_ENABLED static constexpr T result(T base)
0052     {
0053         T power = positive_power<N/2>::result(base);
0054         return base * power * power;
0055     }
0056 };
0057
0058 template <>
0059 struct positive_power<1, 1>
0060 {
0061     template <typename T>
0062     BOOST_MATH_GPU_ENABLED static constexpr T result(T base){ return base; }
0063 };
0064
0065
0066 template <int N, bool>
0067 struct power_if_positive
0068 {
0069     template <typename T, class Policy>
0070     BOOST_MATH_GPU_ENABLED static constexpr T result(T base, const Policy&)
0071     { return positive_power<N>::result(base); }
0072 };
0073
0074 template <int N>
0075 struct power_if_positive<N, false>
0076 {
0077     template <typename T, class Policy>
0078     BOOST_MATH_GPU_ENABLED static constexpr T result(T base, const Policy& policy)
0079     {
0080         if (base == 0)
0081         {
0082             return policies::raise_overflow_error<T>(
0083                        "boost::math::pow(%1%)",
0084                        "Attempted to compute a negative power of 0",
0085                        policy
0086                    );
0087         }
0088
0089         return T(1) / positive_power<-N>::result(base);
0090     }
0091 };
0092
0093 template <>
0094 struct power_if_positive<0, true>
0095 {
0096     template <typename T, class Policy>
0097     BOOST_MATH_GPU_ENABLED static constexpr T result(T base, const Policy& policy)
0098     {
0099         if (base == 0)
0100         {
0101             return policies::raise_indeterminate_result_error<T>(
0102                        "boost::math::pow(%1%)",
0103                        "The result of pow<0>(%1%) is undetermined",
0104                        base,
0105                        T(1),
0106                        policy
0107                    );
0108         }
0109
0110         return T(1);
0111     }
0112 };
0113
0114
0115 template <int N>
0116 struct select_power_if_positive
0117 {
0118     using type = power_if_positive<N, (N >= 0)>;
0119 };
0120
0121
0122 }  // namespace detail
0123
0124
0125 template <int N, typename T, class Policy>
0126 BOOST_MATH_GPU_ENABLED constexpr inline typename tools::promote_args<T>::type pow(T base, const Policy& policy)
0127 {
0128    using result_type = typename tools::promote_args<T>::type;
0129    return detail::select_power_if_positive<N>::type::result(static_cast<result_type>(base), policy);
0130 }
0131
0132 template <int N, typename T>
0133 BOOST_MATH_GPU_ENABLED constexpr inline typename tools::promote_args<T>::type pow(T base)
0134 { return pow<N>(base, policies::policy<>()); }
0135
0136 #ifdef _MSC_VER
0137 #pragma warning(pop)
0138 #endif
0139
0140 }  // namespace math
0141 }  // namespace boost
0142
0143
0144 #endif