cuda::std::complex specializations for half and bfloat

[griwes]

Description

Resolves #1139

Introduce specializations of complex<T> for half and bfloat.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Additional checklist

• The documentation contains the actual release this will be made available in.

[miscco]

That is a great job working around the quirks of those types 👏

I would love to move some of the traits around (e.g. into is_floating_point.h) and importantly add a proper named define that one can grep for.

[gonzalobg]

LGTM in general, thanks for working on this @griwes !
I think I missed some static_asserts for the size and alignment of complex half and bfloat, do we have these somewhere? Thanks!

[miscco]

I am wondering whether we should just keep all the _LIBCUDACXX_HAS_NO_NVFP16 in place and define it conditionally for host

[leofang]

Note: As discussed offline, local tests show that at least on sm86/89 we need this patch for performance reasons. I haven't had a chance to test on sm70/80/90, though.

diff --git a/libcudacxx/include/cuda/std/detail/libcxx/include/complex b/libcudacxx/include/cuda/std/detail/libcxx/include/complex
index 3ba249779..416c0e71d 100644
--- a/libcudacxx/include/cuda/std/detail/libcxx/include/complex
+++ b/libcudacxx/include/cuda/std/detail/libcxx/include/complex
@@ -1702,6 +1702,16 @@ atanh(const complex<_Tp>& __x)
     return complex<_Tp>(__constexpr_copysign(__z.real(), __x.real()), __constexpr_copysign(__z.imag(), __x.imag()));
 }
 
+// we add a specialization for fp16 atanh because of performance issues
+template<>
+_LIBCUDACXX_INLINE_VISIBILITY complex<__half>
+atanh(const complex<__half>& __x)
+{
+    complex<float> __temp(__x);
+    __temp = _CUDA_VSTD::atanh(__temp);
+    return complex<__half>(__temp.real(), __temp.imag());
+}
+
 // sinh
 
 template<class _Tp>
@@ -1815,6 +1825,16 @@ atan(const complex<_Tp>& __x)
     return complex<_Tp>(__z.imag(), -__z.real());
 }
 
+// we add a specialization for fp16 atanh because of performance issues
+template<>
+_LIBCUDACXX_INLINE_VISIBILITY complex<__half>
+atan(const complex<__half>& __x)
+{
+    complex<float> __temp(__x);
+    __temp = _CUDA_VSTD::atan(__temp);
+    return complex<__half>(__temp.real(), __temp.imag());
+}
+
 // sin
 
 template<class _Tp>

[miscco]

@leofang I added some workarounds for asinh acosh atanh and cosh