[libcxx-commits] [PATCH] D59937: Added implementation of expint (Math Special Functions) in std::experimental.

[Andre Brand via Phabricator via libcxx-commits]

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Added implementations of std::expint  as specified in ISO/IEC JTC 1/SC 22/WG 21 N3060 and in the C++17 standard.

The implementation is based on Press, William H., et al. Numerical recipes 3rd edition: The art of scientific computing. Cambridge university press, 2007.

It is tested against the implementations of Visual Studio 2017, boost-1.66, and libstdc++.
Another reference that I check against in the unit tests is the table from Harris, Frank E. "Tables of the exponential integral Ei (x)." Mathematical Tables and Other Aids to Computation 11.57 (1957): 9-16.

There are also tests for analytical bounds for large arguments and arguments close to the singularity.
And we also check the corner cases when +/- infinity or 0 is passed as an argument.

One further note: libstdc++ does not pass all the tests (it produces nan instead of infinity) but Visual Studio 2017 does. boost-1.66 throws overflow errors in these cases.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D59937

Files:
  libcxx/include/experimental/cmath
  libcxx/src/experimental/expint.cpp
  libcxx/test/std/experimental/numerics/c.math/expint_bounds.pass.cpp
  libcxx/test/std/experimental/numerics/c.math/expint_comparisons.pass.cpp
  libcxx/test/std/experimental/numerics/c.math/expint_limits.pass.cpp

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