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/* Translated from Cython into C++ by SciPy developers in 2023.
*
* Original author: Josh Wilson, 2016.
*/
#pragma once
#include "config.h"
namespace xsf {
namespace detail {
XSF_HOST_DEVICE inline std::complex<double> zlog1(std::complex<double> z) {
/* Compute log, paying special attention to accuracy around 1. We
* implement this ourselves because some systems (most notably the
* Travis CI machines) are weak in this regime. */
std::complex<double> coeff = -1.0;
std::complex<double> res = 0.0;
if (std::abs(z - 1.0) > 0.1) {
return std::log(z);
}
z -= 1.0;
for (int n = 1; n < 17; n++) {
coeff *= -z;
res += coeff / static_cast<double>(n);
if (std::abs(res / coeff) < std::numeric_limits<double>::epsilon()) {
break;
}
}
return res;
}
} // namespace detail
} // namespace xsf
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