[Bug c/49595] on amd64, sizeof(__int128_t) > sizeof(intmax_t)

[sandals at crustytoothpaste dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49595

--- Comment #3 from brian m. carlson <sandals at crustytoothpaste dot net> 2011-06-30 18:12:39 UTC ---
(In reply to comment #2)
> sizeof(intmax_t) is fixed by various LP64 ABIs and cannot be changed

That does sound potentially problematic.  I don't see how that solves the
standard conformance issue, though.  If intmax_t cannot be changed, then I
suppose the only appropriate behavior is not to provide any integer types
larger
than intmax_t with -std=c99.

> I believe the stock answer is that __int128 is not a C99 extended integer type,
> so isn't one of the types that intmax_t can represent the value of

There are five *standard signed integer types*.... There may also be
*implementation-defined extended signed integer types*. The standard and
extended signed integer types are collectively called *signed integer types*.

Since the standard specifies intmax_t in terms of a "signed integer type", it
therefore includes any implementation-defined extended signed integer types,
including __int128_t.