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// (C) Copyright John Maddock 2006.
// Use, modification and distribution are subject to the
// Boost Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_MATH_POWM1
#define BOOST_MATH_POWM1
#ifdef _MSC_VER
#pragma once
#endif
#include <boost/math/special_functions/math_fwd.hpp>
#include <boost/math/special_functions/log1p.hpp>
#include <boost/math/special_functions/expm1.hpp>
#include <boost/math/special_functions/trunc.hpp>
#include <boost/assert.hpp>
namespace boost{ namespace math{ namespace detail{
template <class T, class Policy>
inline T powm1_imp(const T x, const T y, const Policy& pol)
{
BOOST_MATH_STD_USING
static const char* function = "boost::math::powm1<%1%>(%1%, %1%)";
if (x > 0)
{
if ((fabs(y * (x - 1)) < 0.5) || (fabs(y) < 0.2))
{
// We don't have any good/quick approximation for log(x) * y
// so just try it and see:
T l = y * log(x);
if (l < 0.5)
return boost::math::expm1(l);
if (l > boost::math::tools::log_max_value<T>())
return boost::math::policies::raise_overflow_error<T>(function, 0, pol);
// fall through....
}
}
else
{
// y had better be an integer:
if (boost::math::trunc(y) != y)
return boost::math::policies::raise_domain_error<T>(function, "For non-integral exponent, expected base > 0 but got %1%", x, pol);
if (boost::math::trunc(y / 2) == y / 2)
return powm1_imp(T(-x), y, pol);
}
return pow(x, y) - 1;
}
} // detail
template <class T1, class T2>
inline typename tools::promote_args<T1, T2>::type
powm1(const T1 a, const T2 z)
{
typedef typename tools::promote_args<T1, T2>::type result_type;
return detail::powm1_imp(static_cast<result_type>(a), static_cast<result_type>(z), policies::policy<>());
}
template <class T1, class T2, class Policy>
inline typename tools::promote_args<T1, T2>::type
powm1(const T1 a, const T2 z, const Policy& pol)
{
typedef typename tools::promote_args<T1, T2>::type result_type;
return detail::powm1_imp(static_cast<result_type>(a), static_cast<result_type>(z), pol);
}
} // namespace math
} // namespace boost
#endif // BOOST_MATH_POWM1
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