Re: [PATCH] inttypes.h: imaxabs(3): Implement as a macro

[Joseph Myers <joseph@codesourcery.com>]

On Tue, 13 Sep 2022, Alejandro Colomar wrote:

> I don't understand the process by which gcc expands builtins.  How does
> exactly the suggested macro interfere with it?  Is it because of the macro?
> Or because of _Generic()?

My point is that you already have to go out of your way to get a link-time 
reference to imaxabs - it will almost always have been expanded inline 
instead.  Given that, your patch is adding extra complexity to address an 
issue that doesn't actually exist.

> That is a workaround to the type being broken.  The type can't widen, due to
> ABI issues; for some time, the compiler provided __int128 as a limbo extension
> that wouldn't be covered by intmax_t, and later ISO C just acknowledged the
> fact and reworded the definition of intmax_t to be less of "the widest type"
> and more or "a wide but not really widest type, so don't really trust it very
> much".

It is the type used for preprocessor arithmetic, for example.

intmax_t was discussed at length in WG14, and while there was agreement on 
reducing its uses (hence the change to floating-point return types for 
fromfp functions, for example, see bug 28327), there was not agreement on 
any particular form of obsolescence.  And it *is* useful in practice for 
printing types such as off_t or mode_t with no corresponding printf 
formats; those could just do with appropriate constraints to be no wider 
than intmax_t when a future POSIX revision is based on C2x.

> If there's no hope in intmax_t, we should just mark the type as obsolescent,
> and discard any idea of having a "widest" type at all.

I don't think it's useful to try to rehash here discussions that were had 
at length in WG14.

> Ahh, you anticipated part 2 of my plan.  Deprecate "j", and add a new set of
> macros PRIdMAX and the like.  This type has it deserved.  But I know those
> macros aren't very well received, so it is just part 2.

The actual direction is to move away from those macros (adding length 
modifiers for printing intN_t / int_leastN_t / int_fastN_t without needing 
to use such macros any more).

-- 
Joseph S. Myers
joseph@codesourcery.com