42 lines
915 B
C++
42 lines
915 B
C++
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// (C) Copyright Matt Borland 2022.
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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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#include <cmath>
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#include <limits>
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#include <boost/math/special_functions/fpclassify.hpp>
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#include <boost/math/constants/constants.hpp>
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namespace boost { namespace math {
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// Calculates log(exp(x1) + exp(x2))
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template <typename Real>
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Real logaddexp(Real x1, Real x2) noexcept
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{
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using std::log1p;
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using std::exp;
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using std::abs;
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// Validate inputs first
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if (!(boost::math::isfinite)(x1))
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{
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return x1;
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}
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else if (!(boost::math::isfinite)(x2))
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{
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return x2;
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}
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const Real temp = x1 - x2;
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if (temp > 0)
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{
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return x1 + log1p(exp(-temp));
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}
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return x2 + log1p(exp(temp));
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}
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}} // Namespace boost::math
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