585da50d7d
This PR adds the code of Boost.Math as of version 1.89 into the third-party directory, as discussed in a recent RFC [1]. The goal is for this code to be used as a back-end for the C++17 Math Special Functions. As explained in third-paty/README.md, this code is cleared for usage inside libc++ for the Math Special functions, however the LLVM Foundation should be consulted before using this code anywhere else in the LLVM project, due to the fact that it is under the Boost Software License (as opposed to the usual LLVM license). See the RFC [1] for more details. [1]: https://discourse.llvm.org/t/rfc-libc-taking-a-dependency-on-boost-math-for-the-c-17-math-special-functions
81 lines
2.0 KiB
C++
81 lines
2.0 KiB
C++
// (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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