Re: [RFC] Add stdckdint.h header for C23

[Joseph Myers <joseph@codesourcery.com>]

On Sat, 10 Jun 2023, Jakub Jelinek via Gcc-patches wrote:

> I have looked at gnulib stdckdint.h and they are full of workarounds
> for various compilers, EDG doesn't do this, clang <= 14 can't multiply
> __int128, ..., so I think the header belongs into the compiler rather
> than C library, because it would be a nightmare to maintain it there.

While C2x only has type-generic macros in this header, there's a proposal 
N2868 (which didn't get consensus for C2x but may come back for a future 
standard version) for additional interfaces for structure types with a 
sticky overflow flag, including some functions that are expected to be 
defined with external linkage as usual for library functions.  So if that 
gets adopted in future, we'd need to arrange to provide those library 
functions with external linkage - which is mostly not something we do in 
GCC, although there are a few atomic_* functions in libatomic in addition 
to the __atomic_* functions underlying type-generic macros.

> What I'm struggling with is enforcing the weird restrictions
> C23 imposes on these.

It's not clear all those restrictions need to be enforced - this 
definitely seems like a case of undefined behavior to provide useful 
extension space, where for various of those restrictions there are unique 
sensible semantics to provide if the types in question are supported.

-- 
Joseph S. Myers
joseph@codesourcery.com