78 lines
1.8 KiB
C++
Executable File
78 lines
1.8 KiB
C++
Executable File
// (C) Copyright John Maddock 2006.
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_MATH_SF_CBRT_HPP
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#define BOOST_MATH_SF_CBRT_HPP
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#ifdef _MSC_VER
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#pragma once
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#endif
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#include <boost/math/tools/roots.hpp>
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#include <boost/math/special_functions/math_fwd.hpp>
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namespace boost{ namespace math{
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namespace detail
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{
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template <class T>
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struct cbrt_functor
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{
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cbrt_functor(T const& target) : a(target){}
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std::tr1::tuple<T, T, T> operator()(T const& z)
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{
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T sqr = z * z;
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return std::tr1::make_tuple(sqr * z - a, 3 * sqr, 6 * z);
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}
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private:
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T a;
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};
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template <class T, class Policy>
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T cbrt_imp(T z, const Policy&)
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{
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BOOST_MATH_STD_USING
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int i_exp, sign(1);
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if(z < 0)
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{
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z = -z;
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sign = -sign;
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}
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if(z == 0)
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return 0;
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frexp(z, &i_exp);
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T min = static_cast<T>(ldexp(0.5, i_exp/3));
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T max = static_cast<T>(ldexp(2.0, i_exp/3));
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T guess = static_cast<T>(ldexp(1.0, i_exp/3));
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int digits = (policies::digits<T, Policy>()) / 2;
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return sign * tools::halley_iterate(detail::cbrt_functor<T>(z), guess, min, max, digits);
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}
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} // namespace detail
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template <class T, class Policy>
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inline typename tools::promote_args<T>::type cbrt(T z, const Policy& pol)
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{
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typedef typename tools::promote_args<T>::type result_type;
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return detail::cbrt_imp(result_type(z), pol);
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}
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template <class T>
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inline typename tools::promote_args<T>::type cbrt(T z)
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{
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return cbrt(z, policies::policy<>());
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}
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} // namespace math
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} // namespace boost
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#endif // BOOST_MATH_SF_CBRT_HPP
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