1 // Boost pow.hpp header file
2 // Computes a power with exponent known at compile-time
3
4 // (C) Copyright Bruno Lalande 2008.
5 // Distributed under the Boost Software License, Version 1.0.
6 // (See accompanying file LICENSE_1_0.txt or copy at
7 // http://www.boost.org/LICENSE_1_0.txt)
8
9 // See http://www.boost.org for updates, documentation, and revision history.
10
11
12 #ifndef BOOST_MATH_POW_HPP
13 #define BOOST_MATH_POW_HPP
14
15
16 #include <boost/math/special_functions/math_fwd.hpp>
17 #include <boost/math/policies/policy.hpp>
18 #include <boost/math/policies/error_handling.hpp>
19 #include <boost/math/tools/promotion.hpp>
20 #include <boost/mpl/greater_equal.hpp>
21
22
23 namespace boost {
24 namespace math {
25
26 #ifdef BOOST_MSVC
27 #pragma warning(push)
28 #pragma warning(disable:4702) // Unreachable code, only triggered in release mode and /W4
29 #endif
30
31 namespace detail {
32
33
34 template <int N, int M = N%2>
35 struct positive_power
36 {
37 template <typename T>
resultboost::math::detail::positive_power38 static BOOST_CXX14_CONSTEXPR T result(T base)
39 {
40 T power = positive_power<N/2>::result(base);
41 return power * power;
42 }
43 };
44
45 template <int N>
46 struct positive_power<N, 1>
47 {
48 template <typename T>
resultboost::math::detail::positive_power49 static BOOST_CXX14_CONSTEXPR T result(T base)
50 {
51 T power = positive_power<N/2>::result(base);
52 return base * power * power;
53 }
54 };
55
56 template <>
57 struct positive_power<1, 1>
58 {
59 template <typename T>
resultboost::math::detail::positive_power60 static BOOST_CXX14_CONSTEXPR T result(T base){ return base; }
61 };
62
63
64 template <int N, bool>
65 struct power_if_positive
66 {
67 template <typename T, class Policy>
resultboost::math::detail::power_if_positive68 static BOOST_CXX14_CONSTEXPR T result(T base, const Policy&)
69 { return positive_power<N>::result(base); }
70 };
71
72 template <int N>
73 struct power_if_positive<N, false>
74 {
75 template <typename T, class Policy>
resultboost::math::detail::power_if_positive76 static BOOST_CXX14_CONSTEXPR T result(T base, const Policy& policy)
77 {
78 if (base == 0)
79 {
80 return policies::raise_overflow_error<T>(
81 "boost::math::pow(%1%)",
82 "Attempted to compute a negative power of 0",
83 policy
84 );
85 }
86
87 return T(1) / positive_power<-N>::result(base);
88 }
89 };
90
91 template <>
92 struct power_if_positive<0, true>
93 {
94 template <typename T, class Policy>
resultboost::math::detail::power_if_positive95 static BOOST_CXX14_CONSTEXPR T result(T base, const Policy& policy)
96 {
97 if (base == 0)
98 {
99 return policies::raise_indeterminate_result_error<T>(
100 "boost::math::pow(%1%)",
101 "The result of pow<0>(%1%) is undetermined",
102 base,
103 T(1),
104 policy
105 );
106 }
107
108 return T(1);
109 }
110 };
111
112
113 template <int N>
114 struct select_power_if_positive
115 {
116 typedef typename mpl::greater_equal<
117 boost::integral_constant<int, N>,
118 boost::integral_constant<int, 0>
119 >::type is_positive;
120
121 typedef power_if_positive<N, is_positive::value> type;
122 };
123
124
125 } // namespace detail
126
127
128 template <int N, typename T, class Policy>
pow(T base,const Policy & policy)129 BOOST_CXX14_CONSTEXPR inline typename tools::promote_args<T>::type pow(T base, const Policy& policy)
130 {
131 typedef typename tools::promote_args<T>::type result_type;
132 return detail::select_power_if_positive<N>::type::result(static_cast<result_type>(base), policy);
133 }
134
135 template <int N, typename T>
pow(T base)136 BOOST_CXX14_CONSTEXPR inline typename tools::promote_args<T>::type pow(T base)
137 { return pow<N>(base, policies::policy<>()); }
138
139 #ifdef BOOST_MSVC
140 #pragma warning(pop)
141 #endif
142
143 } // namespace math
144 } // namespace boost
145
146
147 #endif
148