Add core of c10::complex (#35524)
Summary:
Step 0 of https://github.com/pytorch/pytorch/issues/35284
Reference: https://en.cppreference.com/w/cpp/numeric/complex
We are targeting C++20. The difference across C++ versions are mostly `constexpr` qualifiers, newer version has more function declared as `constexpr`
This PR adds the core of `c10::complex`, it includes
- standard constructors as in `std::complex`
- explicit conversion constructors converting from `std/thrust::complex` to `c10::complex`
- standard assignment operators as in `std::complex`
- conversion assignment operators converting from `std/thrust::complex` to `c10::complex`
- other standard operators as in `std::complex`
- standard methods as in `std::complex`
- explicit casting operators to std/thrust
- basic non-member functions as in `std::complex`:
- arithmetic operators
- `==`, `!=`
- `<<`, `>>`
- `std::real`, `std::imag`, `std::abs`, `std::arg`, `std::norm`, `std::conj`, `std::proj`, `std::polar`
- Some of them are intentionally not completely implemented, these are marked as `TODO` and will be implemented in the future.
This PR does not include:
- overload of math functions
which will come in the next PR
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35524
Differential Revision: D21021677
Pulled By: anjali411
fbshipit-source-id: 9e144e581fa4b2bee62d33adaf756ce5aadc0c71
