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
73 lines
2.6 KiB
C++
73 lines
2.6 KiB
C++
/*
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* Copyright Thomas Dybdahl Ahle, Nick Thompson, Matt Borland, John Maddock, 2023
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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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#ifndef BOOST_MATH_TOOLS_ESTRIN_HPP
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#define BOOST_MATH_TOOLS_ESTRIN_HPP
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#include <array>
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#include <vector>
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#include <type_traits>
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#include <boost/math/tools/assert.hpp>
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namespace boost {
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namespace math {
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namespace tools {
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template <typename RandomAccessContainer1, typename RandomAccessContainer2, typename RealOrComplex>
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inline RealOrComplex evaluate_polynomial_estrin(RandomAccessContainer1 const &coeffs, RandomAccessContainer2 &scratch, RealOrComplex z) {
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// Does anyone care about the complex coefficients, real argument case?
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// I've never seen it used, and this static assert makes the error messages much better:
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static_assert(std::is_same<typename RandomAccessContainer2::value_type, RealOrComplex>::value,
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"The value type of the scratch space must be the same as the abscissa.");
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auto n = coeffs.size();
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BOOST_MATH_ASSERT_MSG(scratch.size() >= (n + 1) / 2, "The scratch space must be at least N+1/2");
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if (n == 0) {
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return static_cast<RealOrComplex>(0);
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}
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for (decltype(n) i = 0; i < n / 2; i++) {
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scratch[i] = coeffs[2 * i] + coeffs[2 * i + 1] * z;
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}
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if (n & 1) {
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scratch[n / 2] = coeffs[n - 1];
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}
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auto m = (n + 1) / 2;
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while (m != 1) {
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z = z * z;
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for (decltype(n) i = 0; i < m / 2; i++) {
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scratch[i] = scratch[2 * i] + scratch[2 * i + 1] * z;
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}
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if (m & 1) {
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scratch[m / 2] = scratch[m - 1];
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}
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m = (m + 1) / 2;
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}
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return scratch[0];
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}
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// The std::array template specialization doesn't need to allocate:
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template <typename RealOrComplex1, size_t n, typename RealOrComplex2>
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inline RealOrComplex2 evaluate_polynomial_estrin(const std::array<RealOrComplex1, n> &coeffs, RealOrComplex2 z) {
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std::array<RealOrComplex2, (n + 1) / 2> ds;
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return evaluate_polynomial_estrin(coeffs, ds, z);
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}
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template <typename RandomAccessContainer, typename RealOrComplex>
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inline RealOrComplex evaluate_polynomial_estrin(const RandomAccessContainer &coeffs, RealOrComplex z) {
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auto n = coeffs.size();
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// Normally, I'd make `ds` a RandomAccessContainer, but its value type needs to be RealOrComplex,
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// and the value_type of the passed RandomAccessContainer can just be Real.
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// Allocation of the std::vector is not ideal, but I have no other ideas at the moment:
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std::vector<RealOrComplex> ds((n + 1) / 2);
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return evaluate_polynomial_estrin(coeffs, ds, z);
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}
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} // namespace tools
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} // namespace math
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} // namespace boost
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#endif
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