ceph/src/boost/boost/math/ccmath/logb.hpp

   1 //  (C) Copyright Matt Borland 2021.
   2 //  Use, modification and distribution are subject to the
   3 //  Boost Software License, Version 1.0. (See accompanying file
   4 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   5
   6 #ifndef BOOST_MATH_CCMATH_LOGB_HPP
   7 #define BOOST_MATH_CCMATH_LOGB_HPP
   8
   9 #include <cmath>
  10 #include <limits>
  11 #include <type_traits>
  12 #include <boost/math/tools/is_constant_evaluated.hpp>
  13 #include <boost/math/ccmath/frexp.hpp>
  14 #include <boost/math/ccmath/isinf.hpp>
  15 #include <boost/math/ccmath/isnan.hpp>
  16 #include <boost/math/ccmath/abs.hpp>
  17
  18 namespace boost::math::ccmath {
  19
  20 namespace detail {
  21
  22 // The value of the exponent returned by std::logb is always 1 less than the exponent returned by
  23 // std::frexp because of the different normalization requirements: for the exponent e returned by std::logb,
  24 // |arg*r^-e| is between 1 and r (typically between 1 and 2), but for the exponent e returned by std::frexp,
  25 // |arg*2^-e| is between 0.5 and 1.
  26 template <typename T>
  27 inline constexpr T logb_impl(T arg) noexcept
  28 {
  29     int exp = 0;
  30     boost::math::ccmath::frexp(arg, &exp);
  31
  32     return exp - 1;
  33 }
  34
  35 } // Namespace detail
  36
  37 template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
  38 inline constexpr Real logb(Real arg) noexcept
  39 {
  40     if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
  41     {
  42         return boost::math::ccmath::abs(arg) == Real(0) ? -std::numeric_limits<Real>::infinity() :
  43                boost::math::ccmath::isinf(arg) ? std::numeric_limits<Real>::infinity() :
  44                boost::math::ccmath::isnan(arg) ? std::numeric_limits<Real>::quiet_NaN() :
  45                boost::math::ccmath::detail::logb_impl(arg);
  46     }
  47     else
  48     {
  49         using std::logb;
  50         return logb(arg);
  51     }
  52 }
  53
  54 template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
  55 inline constexpr double logb(Z arg) noexcept
  56 {
  57     return boost::math::ccmath::logb(static_cast<double>(arg));
  58 }
  59
  60 inline constexpr float logbf(float arg) noexcept
  61 {
  62     return boost::math::ccmath::logb(arg);
  63 }
  64
  65 #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
  66 inline constexpr long double logbl(long double arg) noexcept
  67 {
  68     return boost::math::ccmath::logb(arg);
  69 }
  70 #endif
  71
  72 } // Namespaces
  73
  74 #endif // BOOST_MATH_CCMATH_LOGB_HPP