Re: [RFC] man7/system_data_types.7: Document [unsigned] __int128

From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Alejandro Colomar <colomar.6.4.3@gmail.com>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>,
	"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>,
	linux-man <linux-man@vger.kernel.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Subject: Re: [RFC] man7/system_data_types.7: Document [unsigned] __int128
Date: Thu, 1 Oct 2020 14:46:14 +0100	[thread overview]
Message-ID: <CAH6eHdSO3JYLRtsZWUuNmBJrzW3Hxr3gKuvQ2n=Keba0bu2Dcw@mail.gmail.com> (raw)
In-Reply-To: <9937df9c-f516-eada-682f-a755700231ff@gmail.com>

On Thu, 1 Oct 2020 at 14:22, Alejandro Colomar <colomar.6.4.3@gmail.com> wrote:
>
>
>
> On 2020-10-01 14:54, Szabolcs Nagy wrote:
> > The 10/01/2020 12:14, Alejandro Colomar via Gcc wrote:
> >> Here is the rendered intmax_t:
> >>
> >> intmax_t
> >>        Include: <stdint.h>.  Alternatively, <inttypes.h>.
> >>
> >>        A  signed  integer type capable of representing any value of any
> >>        signed integer type supported by the implementation.   According
> >>        to  the C language standard, it shall be capable of storing val-
> >>        ues in the range [INTMAX_MIN, INTMAX_MAX].
> >>
> >>        The macro INTMAX_C() expands its argument to an integer constant
> >>        of type intmax_t.
> >>
> >>        The  length  modifier  for  intmax_t  for  the printf(3) and the
> >>        scanf(3) families of functions is j; resulting commonly  in  %jd
> >>        or %ji for printing intmax_t values.
> >>
> >>        Bugs:  intmax_t  is not large enough to represent values of type
> >>        __int128 in implementations where __int128 is defined  and  long
> >>        long is less than 128 bits wide.
> >
> > or __int128 is not an integer type.
> >
> > integer types are either standard or extended.
> > and __int128 is neither because it can be
> > larger than intmax_t and stdint.h does not
> > provide the necessary macros for it.
>
>
> Hi Szabolcs,
>
> I know GCC decided to not call it an integer type, and call it instead a
> scalar type, just to conform with the standards, at the same time
> provide a 128 int, and at the same time, not have to change the ABI of
> intmax_t.
>
> But it looks like an integer type,
> and in almost any possible way, it acts like an integer type.
>
> I could call '__int128' a signed _scalar_ type in the description, but
> that might confuse those who don't know these details.  Do you think it
> would be better to call it that way, or just keep the integer word?
> (Jonathan, I'd also like to know your thoughts on this, BTW).

I hope WG14 will adopt something like
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2465.pdf and the
whole mess will go away.

intmax_t will be deprecated, and implementations can provide 128-bit
integers without caveats.