[PATCH] Introduce hardbool attribute for C

[Thomas Koenig]

Hi Alexandre,

> On Apr  6, 2023, Bernhard Reutner-Fischer <rep.dot.nop@gmail.com> wrote:
> 
>> 29 For C_BOOL, the internal representation of .TRUE._C_BOOL and
>> .FALSE._C_BOOL shall be the same as those of
>> 30 the C values (_Bool)1 and (_Bool)0 respectively.
> 
> I'm not changing any of the standard types, FWIW.  The proposed
> extension enables alternate boolean types to be introduced, with
> extra checking for hardening.
> 
>> I personally like your proposed 0 and ~0, that's probably pretty robust.
> 
> That is only a default.  Certain applications may benefit from other
> values.  0xa5 and 0x5a seem to make a good combination too.
In gfortran, we depend on the representation of 0/1 for several things
(among them avoiding having separate library versions for logical
kind=1,2,4,8,16 for MASK).

So, such a type would be incompatible with vanilla LOGICAL variables
and with C interop logical variables.

If anybody should pass such a hardbool variable to Fortran, they
will get unpredictable results, and deserve to lose.  The opposite
effect of what would be intended :-)

Best regards

	Thomas