Re: [musl] [PATCH] vfprintf: support C2x %b and %B conversion specifiers

["Jₑₙₛ Gustedt" <jens.gustedt@inria.fr>]

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Rich,

on Tue, 20 Sep 2022 10:46:18 -0400 you (Rich Felker <dalias@libc.org>)
wrote:

> On Tue, Sep 20, 2022 at 04:27:28PM +0200, Jₑₙₛ Gustedt wrote:
> > on Tue, 20 Sep 2022 16:22:36 +0200 you (Jₑₙₛ Gustedt
> > <jens.gustedt@inria.fr>) wrote:
> >   
> > > There is a feature test macro for the maximum width of bit-precise
> > > integers, `BITINT_MAXWIDTH`. It is guaranteed to be at least
> > > `ULLONG_WIDTH` but can (and will) be larger on many platforms.  
> > 
> > e.g on my ubuntu-nothing-fancy machine I get
> > 
> >  clang -E -dM -xc /dev/null | grep -i bitint
> >  #define __BITINT_MAXWIDTH__ 128  
> 
> As I understand it, that gives the application knowledge of what
> bit-precise types the compiler can provide to it, but doesn't do
> anything to tell the application what wN modifiers printf can be
> expected to support. If it were required to support wN for
> N==BITINT_MAXWIDTH that would at least be something to go from, but I
> see no such requirement and I'm not sure it's desirable (it means you
> can't let the compiler offer larger BITINT_MAXWIDTH, but would have to
> define it as what libc supports).
> 
> I think a separate macro indicating what printf supports is needed to
> solve this problem well.

That's an excellent point. It would be good if we filed a national
body comment for the ballot period to get such a thing in.

Jₑₙₛ

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