Re: 128-bit integers and intmax_t

[Geoff Keating <geoffk at cygnus dot com>]

"Joseph S. Myers" <jsm28@cam.ac.uk> writes:

> When HOST_BITS_PER_WIDE_INT >= 64, gcc has some support for 128-bit
> integer types (`int __attribute__((__mode__(__TI__)))' and `unsigned int
> __attribute__((__mode__(__TI__)))').  Should these count as "extended
> integer types" (within the meaning of C99 6.2.5p7)?
> 
> If they so count, then intmax_t and uintmax_t would need to be defined
> accordingly - which would break existing ABIs (e.g. glibc), and the
> dependence on HOST_BITS_PER_WIDE_INT would be rather undesirable.  The
> pragmatic solution seems to be to define that these types are not extended
> integer types, regardless of the level of support GCC has for them and how
> much they look like extended integer types, and to add appropriate
> -pedantic warnings, but does anyone see any better solution?

This is a libc issue.  They are extended integer types if and only if
the libc defines intmax_t (or some other standard type) as them.
Otherwise, there's no way for a strictly conforming C program to know
they exist.

-- 
- Geoffrey Keating <geoffk@cygnus.com>