P1467R9 Extended Floating-Point Types

[StephanTLavavej]

Fixes #2956.

• <stdfloat> contains a couple of comments explaining why it's almost, but not completely, empty.
  • All of the push-pop machinery is extremely intentional - it is important that every header contains this machinery, so that we won't introduce errors during later maintenance or copy-pasting.
• I'm adding this to the Core section of <__msvc_all_public_headers.hpp>.
• <yvals_core.h> contains a clarifying comment, so that readers will understand what we're claiming to support.
• I don't think we need to add a dedicated test for this. Technically, the include-each-header-alone, header units, and modules tests aren't verifying that <stdfloat> itself provides namespace std, but the comment in the header ensures that we won't remove this during maintenance. It doesn't seem to be worth spending further test throughput to verify one of the world's emptiest headers.

[CaseyCarter]

In WG21-P1467R9, 9.3.6 adds a requirement that specializations of std::complex are trivially-copyable; should we have test coverage?

[StephanTLavavej]

@strega-nil-ms @CaseyCarter I've pushed test coverage as requested, after finding the best place to add it.

[CaseyCarter]

Approved harder!

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[TautologicalContradiction]

I think at least std::float32_t and std::float64_t should be implemented atm, both could be aliases to float and double respectively, since these two types based on the MSVC's implementation, accomplish the requirements of std::float32_t and std::float64_t

[frederick-vs-ja]

I think at least std::float32_t and std::float64_t should be implemented atm, both could be aliases to float and double respectively, since these two types based on the MSVC's implementation, accomplish the requirements of std::float32_t and std::float64_t

This is not allowed by the standard. float and double are standard floating-point types, while std::float32_t and std::float64_t are extended floating-point types, so they must be distinct.

I want to add std::float16_t (i.e. _Float16) support for Clang (perhaps together with EDG), but maintainers seemly don't like doing so until MSVC supports std::float16_t.

[2bitsin]

What is the actual point of adding this header if it does not contain std::float32_t or std::float64_t atleast...

[CaseyCarter]

What is the actual point of adding this header if it does not contain std::float32_t or std::float64_t atleast...

We don't design the Standard Library, we just implement it. The working draft for the C++23 Standard says this header exists - it's not optional - so here it is.