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
23namespace boost {
24namespace 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
31namespace detail {
32
33
34template <int N, int M = N%2>
35struct positive_power
36{
37 template <typename T>
38 static T result(T base)
39 {
40 T power = positive_power<N/2>::result(base);
41 return power * power;
42 }
43};
44
45template <int N>
46struct positive_power<N, 1>
47{
48 template <typename T>
49 static T result(T base)
50 {
51 T power = positive_power<N/2>::result(base);
52 return base * power * power;
53 }
54};
55
56template <>
57struct positive_power<1, 1>
58{
59 template <typename T>
60 static T result(T base){ return base; }
61};
62
63
64template <int N, bool>
65struct power_if_positive
66{
67 template <typename T, class Policy>
68 static T result(T base, const Policy&)
69 { return positive_power<N>::result(base); }
70};
71
72template <int N>
73struct power_if_positive<N, false>
74{
75 template <typename T, class Policy>
76 static 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
91template <>
92struct power_if_positive<0, true>
93{
94 template <typename T, class Policy>
95 static 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
113template <int N>
114struct 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
128template <int N, typename T, class Policy>
129inline 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
136template <int N, typename T>
137inline typename tools::promote_args<T>::type pow(T base)
138{ return pow<N>(base, policies::policy<>()); }
139
140#ifdef BOOST_MSVC
141#pragma warning(pop)
142#endif
143
144} // namespace math
145} // namespace boost
146
147
148#endif
149

source code of include/boost/math/special_functions/pow.hpp