Re: [PATCH 3/4] use exact types for the [U]INTXX_C macros

[Jens Gustedt <jens.gustedt@inria.fr>]

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Am Dienstag, den 02.12.2014, 13:03 -0500 schrieb Rich Felker:
> On Tue, Nov 25, 2014 at 03:50:06PM +0100, Jens Gustedt wrote:
> > The C standard requires the exact types [u]int_leastXX_t for these
> > macros in 7.20.4.1
> 
> You've misread the standard, and I did too originally. This was fixed
> in commit a591e0383a0a31ac94541846796b93fedc63a0c4. The relevant text
> is (C99 7.18.4 or C11 7.20.4, paragraph 3):
> 
> "Each invocation of one of these macros shall expand to an integer
> constant expression suitable for use in #if preprocessing directives.
> The type of the expression shall have the same type as would an
> expression of the corresponding type converted according to the
> integer promotions. The value of the expression shall be that of the
> argument."
> 
> In the text you're looking at:
> 
> "The macro INTN_C(value) shall expand to an integer constant
> expression corresponding to the type int_leastN_t. The macro
> UINTN_C(value) shall expand to an integer constant expression
> corresponding to the type uint_leastN_t. For example, if
> uint_least64_t is a name for the type unsigned long long int, then
> UINT64_C(0x123) might expand to the integer constant 0x123ULL."
> 
> the "correspondence" referred to by "corresponding" should be
> interpreted as the one via integer promotions in the above text I
> cited.

No, that doesn't seem to be the view of the committee on that
issue. There is a ongoing DR on that and the consensus of the
committee in the discussion seems to be that this is the required
type, e.g to be usable in _Generic.

The only ambiguity there seemed to be that they were convinced that
this needs internal compiler magic to be achieved, which isn't the
case.

> IMO this part of the standard is horribly worded, and I would love to
> get it improved, because this topic comes up again and again.

agreed

Jens

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