Hi Jonathan,
On 2020-10-01 11:57, Jonathan Wakely wrote:
> On Thu, 1 Oct 2020 at 10:26, Alejandro Colomar via Gcc
<gcc@xxxxxxxxxxx> wrote:
>>
>> Hi,
>>
>> I'm documenting the system data types in the man-pages,
>> and I was writing now about these types.
>>
>> I'm showing below both the rendered output and the source I have
right now.
>>
>> Would you add anything to it?
>>
>> And I have some questions:
>>
>> Is 'signed __int128' a valid thing,
>> and if so is it completely equivalent to '__int128'?
>
> Yes.
>
>> Is the GCC version correct?
>>
>> There's no implementation where 'long long' is 128 bits yet, right?
>
> Right.
>
>> Thanks,
>>
>> Alex
>>
>> Rendered output:
>> [[
>> __int128
>> A signed integer type of a fixed width of exactly 128 bits.
>>
>> According to GNU, it is supported only for targets which have an
>> integer mode wide enough to hold 128 bits.
>
> "According to GNU"? Should that be GCC?
>
> The GNU project doesn't have anything to say about it.
>
> Maybe just "When using GCC, it is supported only ..."
Ok, I thought that GCC is part of the GNU project, but I don't know how
much...
I'll use "When using GCC," :)
>
>
>>
>> Bugs: It is not possible to express an integer constant of type
>> __int128 in implementations where long long is less than 128
>> bits wide.
>>
>> Conforming to: GCC 4.6.0 and later.
>
> It doesn't conform to anything, shouldn't this say "This type is a GNU
> extension." or just "This type is an extension." ?
That's what I had first: "Conforming to: GCC extension"
Then I thought that I could include the version information,
so I changed it to that.
Maybe "GCC extension (since GCC 4.6.0)" would be better?
>
>>
>> Notes: This type is available without including any header.
>>
>> See also the intmax_t, intN_t and unsigned __int128 types in
>> this page.
>
> Why would this type refer to intmax_t?
>
Because 'intmax_t' has a bug
(actually I know GCC rejected the bug report,
but the problem is still there and users should be informed about this)
which is related to __int128.
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.
Conforming to: C99 and later; POSIX.1-2001 and later.
See also the uintmax_t type in this page.
Thanks,
Alex
