math/ccmath/floor.hpp

0001 //  (C) Copyright Matt Borland 2021.
0002 //  Use, modification and distribution are subject to the
0003 //  Boost Software License, Version 1.0. (See accompanying file
0004 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0005
0006 #ifndef BOOST_MATH_CCMATH_FLOOR_HPP
0007 #define BOOST_MATH_CCMATH_FLOOR_HPP
0008
0009 #include <boost/math/ccmath/detail/config.hpp>
0010
0011 #ifdef BOOST_MATH_NO_CCMATH
0012 #error "The header <boost/math/floor.hpp> can only be used in C++17 and later."
0013 #endif
0014
0015 #include <boost/math/ccmath/abs.hpp>
0016 #include <boost/math/ccmath/isinf.hpp>
0017 #include <boost/math/ccmath/isnan.hpp>
0018 #include <limits>
0019
0020 namespace boost::math::ccmath {
0021
0022 namespace detail {
0023
0024 template <typename T>
0025 inline constexpr T floor_pos_impl(T arg) noexcept
0026 {
0027     constexpr auto max_comp_val = T(1) / std::numeric_limits<T>::epsilon();
0028
0029     if (arg >= max_comp_val)
0030     {
0031         return arg;
0032     }
0033
0034     T result = 1;
0035
0036     if(result < arg)
0037     {
0038         while(result < arg)
0039         {
0040             result *= 2;
0041         }
0042         while(result > arg)
0043         {
0044             --result;
0045         }
0046
0047         return result;
0048     }
0049     else
0050     {
0051         return T(0);
0052     }
0053 }
0054
0055 template <typename T>
0056 inline constexpr T floor_neg_impl(T arg) noexcept
0057 {
0058     T result = -1;
0059
0060     if(result > arg)
0061     {
0062         while(result > arg)
0063         {
0064             result *= 2;
0065         }
0066         while(result < arg)
0067         {
0068             ++result;
0069         }
0070         if(result != arg)
0071         {
0072             --result;
0073         }
0074     }
0075
0076     return result;
0077 }
0078
0079 template <typename T>
0080 inline constexpr T floor_impl(T arg) noexcept
0081 {
0082     if(arg > 0)
0083     {
0084         return floor_pos_impl(arg);
0085     }
0086     else
0087     {
0088         return floor_neg_impl(arg);
0089     }
0090 }
0091
0092 } // Namespace detail
0093
0094 template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
0095 inline constexpr Real floor(Real arg) noexcept
0096 {
0097     if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
0098     {
0099         return boost::math::ccmath::abs(arg) == Real(0) ? arg :
0100                boost::math::ccmath::isinf(arg) ? arg :
0101                boost::math::ccmath::isnan(arg) ? arg :
0102                boost::math::ccmath::detail::floor_impl(arg);
0103     }
0104     else
0105     {
0106         using std::floor;
0107         return floor(arg);
0108     }
0109 }
0110
0111 template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
0112 inline constexpr double floor(Z arg) noexcept
0113 {
0114     return boost::math::ccmath::floor(static_cast<double>(arg));
0115 }
0116
0117 inline constexpr float floorf(float arg) noexcept
0118 {
0119     return boost::math::ccmath::floor(arg);
0120 }
0121
0122 #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
0123 inline constexpr long double floorl(long double arg) noexcept
0124 {
0125     return boost::math::ccmath::floor(arg);
0126 }
0127 #endif
0128
0129 } // Namespaces
0130
0131 #endif // BOOST_MATH_CCMATH_FLOOR_HPP