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Date: Thu, 27 Aug 2015 09:42:00 -0000
From: Marc Glisse <marc.glisse@inria.fr>
Reply-To: gcc-help@gcc.gnu.org
To: Jonathan Wakely <jwakely.gcc@gmail.com>
cc: David Brown <david@westcontrol.com>, Martin Sebor <msebor@gmail.com>,     Kostas Savvidis <ksavvidis@gmail.com>, gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: 128-bit integer - nonsensical documentation?
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On Thu, 27 Aug 2015, Jonathan Wakely wrote:

>> Are you allowed to include typedefs for uint128_t and int128_t in
>> <stdint.h>, or would that also only be allowed if it is a proper
>> extended integer?
>
> Those names are not in the namespace reserved for the implementation,
> so doing that would cause this valid code to fail to compile:
>
> #include <stdint.h>
> typedef struct { } uint128_t;
> int main() { }

C11
7.31 Future library directions
7.31.10 Integer types <stdint.h>
Typedef names beginning with int or uint and ending with _t may be added 
to the types defined in the <stdint.h> header.

7.20.1.1 also gives restrictions on the semantics of any type called 
uintN_t.

I would interpret that as making your program non-portable, if not broken.

-- 
Marc Glisse