[cfe-commits] [PATCH] Improved handling of 128-bit integer literals

[Stephen Canon]

On Nov 29, 2012, at 8:23 PM, Chris Lattner <clattner at apple.com> wrote:

> On Nov 29, 2012, at 4:23 PM, Stephen Canon <scanon at apple.com> wrote:
> 
>> On Nov 29, 2012, at 7:16 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>> 
>>> Generally, we still need to handle Eli's observation that the C and C++ extended integer type rules require us to make intmax_t be __int128 if we're going to allow literals to be of type __int128. I'm inclined to say we should bite the bullet here, and treat __int128 as a proper extended integer type (and thus change intmax_t, preprocessor constant expressions, and so on). Any objections?
>> 
>> In the long run, I would very much like for intmax_t to be 128-bits where we can do so, but it's a *major* undertaking.  In particular, it requires considerable platform library support; off the top of my head:
>> 
>> • libc needs to be able to printf/scanf intmax_t via SCN*MAX / PRI*MAX, and needs to support strtoimax, etc.
>> • libc needs to support imaxdiv and imaxabs.
>> 
>> This will cause a decent amount of binary-compatibility headaches.  It's a goal worth aiming for, but it's a good ways off still.
> 
> I agree, it's a great goal, but it will be a massive undertaking.

In the meantime, if we're really worried about conformance, here perhaps -std=c99,c11,c++11, etc should disable __[u]int128_t?  (Though this would likely cause a hassle for some users).

- Steve