81 lines
2.0 KiB
C++
81 lines
2.0 KiB
C++
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// (C) Copyright Matt Borland 2021.
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Constexpr implementation of sqrt function
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#ifndef BOOST_MATH_CCMATH_SQRT
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#define BOOST_MATH_CCMATH_SQRT
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#include <boost/math/ccmath/detail/config.hpp>
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#ifdef BOOST_MATH_NO_CCMATH
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#error "The header <boost/math/sqrt.hpp> can only be used in C++17 and later."
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#endif
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#include <boost/math/ccmath/abs.hpp>
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#include <boost/math/ccmath/isnan.hpp>
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#include <boost/math/ccmath/isinf.hpp>
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#include <boost/math/tools/is_constant_evaluated.hpp>
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namespace boost::math::ccmath {
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namespace detail {
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template <typename Real>
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constexpr Real sqrt_impl_2(Real x, Real s, Real s2)
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{
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return !(s < s2) ? s2 : sqrt_impl_2(x, (x / s + s) / 2, s);
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}
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template <typename Real>
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constexpr Real sqrt_impl_1(Real x, Real s)
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{
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return sqrt_impl_2(x, (x / s + s) / 2, s);
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}
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template <typename Real>
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constexpr Real sqrt_impl(Real x)
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{
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return sqrt_impl_1(x, x > 1 ? x : Real(1));
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}
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} // namespace detail
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template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
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constexpr Real sqrt(Real x)
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{
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if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
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{
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if (boost::math::ccmath::isnan(x) ||
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(boost::math::ccmath::isinf(x) && x > 0) ||
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boost::math::ccmath::abs(x) == Real(0))
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{
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return x;
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}
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// Domain error is implementation defined so return NAN
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else if (boost::math::ccmath::isinf(x) && x < 0)
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{
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return std::numeric_limits<Real>::quiet_NaN();
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}
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return detail::sqrt_impl<Real>(x);
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}
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else
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{
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using std::sqrt;
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return sqrt(x);
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}
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}
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template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
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constexpr double sqrt(Z x)
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{
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return detail::sqrt_impl<double>(static_cast<double>(x));
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}
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} // Namespaces
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#endif // BOOST_MATH_CCMATH_SQRT
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