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
21 namespace boost{ namespace math{ namespace detail{
22
23 template <class T, class Policy>
powm1_imp(const T x,const T y,const Policy & pol)24 inline 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, pol);
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
56 template <class T1, class T2>
57 inline typename tools::promote_args<T1, T2>::type
powm1(const T1 a,const T2 z)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
64 template <class T1, class T2, class Policy>
65 inline typename tools::promote_args<T1, T2>::type
powm1(const T1 a,const T2 z,const Policy & pol)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
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