1// (C) Copyright John Maddock 2006.
2// Use, modification and distribution are subject to the
3// Boost Software License, Version 1.0. (See accompanying file
4// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5
6#ifndef BOOST_MATH_POWM1
7#define BOOST_MATH_POWM1
8
9#ifdef _MSC_VER
10#pragma once
11#pragma warning(push)
12#pragma warning(disable:4702) // Unreachable code (release mode only warning)
13#endif
14
15#include <boost/math/special_functions/math_fwd.hpp>
16#include <boost/math/special_functions/log1p.hpp>
17#include <boost/math/special_functions/expm1.hpp>
18#include <boost/math/special_functions/trunc.hpp>
19#include <boost/assert.hpp>
20
21namespace boost{ namespace math{ namespace detail{
22
23template <class T, class Policy>
24inline T powm1_imp(const T x, const T y, const Policy& pol)
25{
26 BOOST_MATH_STD_USING
27 static const char* function = "boost::math::powm1<%1%>(%1%, %1%)";
28
29 if (x > 0)
30 {
31 if ((fabs(y * (x - 1)) < 0.5) || (fabs(y) < 0.2))
32 {
33 // We don't have any good/quick approximation for log(x) * y
34 // so just try it and see:
35 T l = y * log(x);
36 if (l < 0.5)
37 return boost::math::expm1(l);
38 if (l > boost::math::tools::log_max_value<T>())
39 return boost::math::policies::raise_overflow_error<T>(function, 0, pol);
40 // fall through....
41 }
42 }
43 else
44 {
45 // y had better be an integer:
46 if (boost::math::trunc(y) != y)
47 return boost::math::policies::raise_domain_error<T>(function, "For non-integral exponent, expected base > 0 but got %1%", x, pol);
48 if (boost::math::trunc(y / 2) == y / 2)
49 return powm1_imp(T(-x), y, pol);
50 }
51 return pow(x, y) - 1;
52}
53
54} // detail
55
56template <class T1, class T2>
57inline typename tools::promote_args<T1, T2>::type
58 powm1(const T1 a, const T2 z)
59{
60 typedef typename tools::promote_args<T1, T2>::type result_type;
61 return detail::powm1_imp(static_cast<result_type>(a), static_cast<result_type>(z), policies::policy<>());
62}
63
64template <class T1, class T2, class Policy>
65inline typename tools::promote_args<T1, T2>::type
66 powm1(const T1 a, const T2 z, const Policy& pol)
67{
68 typedef typename tools::promote_args<T1, T2>::type result_type;
69 return detail::powm1_imp(static_cast<result_type>(a), static_cast<result_type>(z), pol);
70}
71
72} // namespace math
73} // namespace boost
74
75#ifdef _MSC_VER
76#pragma warning(pop)
77#endif
78
79#endif // BOOST_MATH_POWM1
80
81
82
83
84
85

source code of include/boost/math/special_functions/powm1.hpp