87 lines
2.3 KiB
C++
87 lines
2.3 KiB
C++
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// (C) Copyright Matt Borland 2021.
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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_CCMATH_LOGB_HPP
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#define BOOST_MATH_CCMATH_LOGB_HPP
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#include <boost/math/ccmath/detail/config.hpp>
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#ifdef BOOST_MATH_NO_CCMATH
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#error "The header <boost/math/logb.hpp> can only be used in C++17 and later."
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#endif
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#include <boost/math/ccmath/frexp.hpp>
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#include <boost/math/ccmath/isinf.hpp>
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#include <boost/math/ccmath/isnan.hpp>
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#include <boost/math/ccmath/abs.hpp>
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namespace boost::math::ccmath {
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namespace detail {
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// The value of the exponent returned by std::logb is always 1 less than the exponent returned by
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// std::frexp because of the different normalization requirements: for the exponent e returned by std::logb,
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// |arg*r^-e| is between 1 and r (typically between 1 and 2), but for the exponent e returned by std::frexp,
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// |arg*2^-e| is between 0.5 and 1.
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template <typename T>
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constexpr T logb_impl(T arg) noexcept
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{
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int exp = 0;
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boost::math::ccmath::frexp(arg, &exp);
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return static_cast<T>(exp - 1);
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}
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} // Namespace detail
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template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
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constexpr Real logb(Real arg) noexcept
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{
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if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
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{
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if (boost::math::ccmath::abs(arg) == Real(0))
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{
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return -std::numeric_limits<Real>::infinity();
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}
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else if (boost::math::ccmath::isinf(arg))
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{
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return std::numeric_limits<Real>::infinity();
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}
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else if (boost::math::ccmath::isnan(arg))
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{
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return arg;
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}
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return boost::math::ccmath::detail::logb_impl(arg);
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}
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else
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{
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using std::logb;
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return logb(arg);
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}
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}
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template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
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constexpr double logb(Z arg) noexcept
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{
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return boost::math::ccmath::logb(static_cast<double>(arg));
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}
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constexpr float logbf(float arg) noexcept
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{
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return boost::math::ccmath::logb(arg);
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}
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#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
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constexpr long double logbl(long double arg) noexcept
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{
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return boost::math::ccmath::logb(arg);
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}
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#endif
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} // Namespaces
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#endif // BOOST_MATH_CCMATH_LOGB_HPP
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