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// (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 <boost/math/ccmath/detail/config.hpp>
#ifdef BOOST_MATH_NO_CCMATH
#error "The header <boost/math/logb.hpp> can only be used in C++17 and later."
#endif
#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>
constexpr T logb_impl(T arg) noexcept
{
int exp = 0;
boost::math::ccmath::frexp(arg, &exp);
return static_cast<T>(exp - 1);
}
} // Namespace detail
template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
constexpr Real logb(Real arg) noexcept
{
if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
{
if (boost::math::ccmath::abs(arg) == Real(0))
{
return -std::numeric_limits<Real>::infinity();
}
else if (boost::math::ccmath::isinf(arg))
{
return std::numeric_limits<Real>::infinity();
}
else if (boost::math::ccmath::isnan(arg))
{
return arg;
}
return 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>
constexpr double logb(Z arg) noexcept
{
return boost::math::ccmath::logb(static_cast<double>(arg));
}
constexpr float logbf(float arg) noexcept
{
return boost::math::ccmath::logb(arg);
}
#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
constexpr long double logbl(long double arg) noexcept
{
return boost::math::ccmath::logb(arg);
}
#endif
} // Namespaces
#endif // BOOST_MATH_CCMATH_LOGB_HPP
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