49 lines
1.2 KiB
C++
49 lines
1.2 KiB
C++
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// (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_SQRT1PM1
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#define BOOST_MATH_SQRT1PM1
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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/special_functions/math_fwd.hpp>
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#include <boost/math/special_functions/log1p.hpp>
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#include <boost/math/special_functions/expm1.hpp>
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//
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// This algorithm computes sqrt(1+x)-1 for small x:
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//
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namespace boost{ namespace math{
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template <class T, class Policy>
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inline typename tools::promote_args<T>::type sqrt1pm1(const T& val, const Policy& pol)
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{
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typedef typename tools::promote_args<T>::type result_type;
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BOOST_MATH_STD_USING
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if(fabs(result_type(val)) > 0.75)
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return sqrt(1 + result_type(val)) - 1;
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return boost::math::expm1(boost::math::log1p(val, pol) / 2, pol);
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}
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template <class T>
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inline typename tools::promote_args<T>::type sqrt1pm1(const T& val)
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{
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return sqrt1pm1(val, 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_SQRT1PM1
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