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File: logb.hpp
// (C) Copyright Matt Borland 2021. // 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_CCMATH_LOGB_HPP #define BOOST_MATH_CCMATH_LOGB_HPP #include <cmath> #include <limits> #include <type_traits> #include <boost/math/tools/is_constant_evaluated.hpp> #include <boost/math/ccmath/frexp.hpp> #include <boost/math/ccmath/isinf.hpp> #include <boost/math/ccmath/isnan.hpp> #include <boost/math/ccmath/abs.hpp> namespace boost::math::ccmath { namespace detail { // The value of the exponent returned by std::logb is always 1 less than the exponent returned by // std::frexp because of the different normalization requirements: for the exponent e returned by std::logb, // |arg*r^-e| is between 1 and r (typically between 1 and 2), but for the exponent e returned by std::frexp, // |arg*2^-e| is between 0.5 and 1. template <typename T> inline constexpr T logb_impl(T arg) noexcept { int exp = 0; boost::math::ccmath::frexp(arg, &exp); return exp - 1; } } // Namespace detail template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true> inline constexpr Real logb(Real arg) noexcept { if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg)) { return boost::math::ccmath::abs(arg) == Real(0) ? -std::numeric_limits<Real>::infinity() : boost::math::ccmath::isinf(arg) ? std::numeric_limits<Real>::infinity() : boost::math::ccmath::isnan(arg) ? std::numeric_limits<Real>::quiet_NaN() : boost::math::ccmath::detail::logb_impl(arg); } else { using std::logb; return logb(arg); } } template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true> inline constexpr double logb(Z arg) noexcept { return boost::math::ccmath::logb(static_cast<double>(arg)); } inline constexpr float logbf(float arg) noexcept { return boost::math::ccmath::logb(arg); } #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS inline constexpr long double logbl(long double arg) noexcept { return boost::math::ccmath::logb(arg); } #endif } // Namespaces #endif // BOOST_MATH_CCMATH_LOGB_HPP