Added thirdparty: boost library

thirdparty/include/boost/math/tools/estrin.hpp

@@ -0,0 +1,72 @@
+/*
+ * Copyright Thomas Dybdahl Ahle, Nick Thompson, Matt Borland, John Maddock, 2023
+ * Use, modification and distribution are subject to the
+ * Boost Software License, Version 1.0. (See accompanying file
+ * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+#ifndef BOOST_MATH_TOOLS_ESTRIN_HPP
+#define BOOST_MATH_TOOLS_ESTRIN_HPP
+
+#include <array>
+#include <vector>
+#include <type_traits>
+#include <boost/math/tools/assert.hpp>
+
+namespace boost {
+namespace math {
+namespace tools {
+
+template <typename RandomAccessContainer1, typename RandomAccessContainer2, typename RealOrComplex>
+inline RealOrComplex evaluate_polynomial_estrin(RandomAccessContainer1 const &coeffs, RandomAccessContainer2 &scratch, RealOrComplex z) {
+  // Does anyone care about the complex coefficients, real argument case?
+  // I've never seen it used, and this static assert makes the error messages much better:
+  static_assert(std::is_same<typename RandomAccessContainer2::value_type, RealOrComplex>::value,
+                "The value type of the scratch space must be the same as the abscissa.");
+  auto n = coeffs.size();
+  BOOST_MATH_ASSERT_MSG(scratch.size() >= (n + 1) / 2, "The scratch space must be at least N+1/2");
+
+  if (n == 0) {
+    return static_cast<RealOrComplex>(0);
+  }
+  for (decltype(n) i = 0; i < n / 2; i++) {
+    scratch[i] = coeffs[2 * i] + coeffs[2 * i + 1] * z;
+  }
+  if (n & 1) {
+    scratch[n / 2] = coeffs[n - 1];
+  }
+  auto m = (n + 1) / 2;
+
+  while (m != 1) {
+    z = z * z;
+    for (decltype(n) i = 0; i < m / 2; i++) {
+      scratch[i] = scratch[2 * i] + scratch[2 * i + 1] * z;
+    }
+    if (m & 1) {
+      scratch[m / 2] = scratch[m - 1];
+    }
+    m = (m + 1) / 2;
+  }
+  return scratch[0];
+}
+
+// The std::array template specialization doesn't need to allocate:
+template <typename RealOrComplex1, size_t n, typename RealOrComplex2>
+inline RealOrComplex2 evaluate_polynomial_estrin(const std::array<RealOrComplex1, n> &coeffs, RealOrComplex2 z) {
+  std::array<RealOrComplex2, (n + 1) / 2> ds;
+  return evaluate_polynomial_estrin(coeffs, ds, z);
+}
+
+template <typename RandomAccessContainer, typename RealOrComplex>
+inline RealOrComplex evaluate_polynomial_estrin(const RandomAccessContainer &coeffs, RealOrComplex z) {
+  auto n = coeffs.size();
+  // Normally, I'd make `ds` a RandomAccessContainer, but its value type needs to be RealOrComplex,
+  // and the value_type of the passed RandomAccessContainer can just be Real.
+  // Allocation of the std::vector is not ideal, but I have no other ideas at the moment:
+  std::vector<RealOrComplex> ds((n + 1) / 2);
+  return evaluate_polynomial_estrin(coeffs, ds, z);
+}
+
+} // namespace tools
+} // namespace math
+} // namespace boost
+#endif