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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_COMMON_STD_CMATH_HH
#define DUNE_COMMON_STD_CMATH_HH
#include <cmath>
#if __has_include(<version>)
#include <version>
#if (__cpp_lib_constexpr_cmath < 202306L)
#include <limits>
#include <type_traits>
#include <utility>
#endif
#endif
namespace Dune {
namespace Std {
#if (__cpp_lib_constexpr_cmath < 202202L)
// backport for constexpr functions between C++20 and C++23
template<class T>
constexpr T
abs(T t)
{
if (std::is_constant_evaluated()) {
return (t < 0) ? -t : t;
} else {
using std::abs;
return abs(t);
}
}
template<class T>
constexpr auto
sqrt(T t)
requires(std::is_floating_point_v<T> || std::is_integral_v<T>)
{
if (std::is_constant_evaluated()) {
using TT = std::conditional_t<std::is_floating_point_v<T>, T, double>;
if (t >= TT{ 0 } and t < std::numeric_limits<TT>::infinity()) {
// use Heron's method:
// https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Heron's_method
TT curr = t, prev = 0;
while (curr != prev)
prev = std::exchange(curr, TT{ 0.5 } * (curr + TT{ t } / curr));
return curr;
} else {
return std::numeric_limits<TT>::quiet_NaN();
}
} else {
using std::sqrt;
return sqrt(t);
}
};
#else
using std::abs;
using std::sqrt;
#endif
} // namespace Std
} // namespace Dune
#endif // #ifndef DUNE_COMMON_STD_CMATH_HH
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