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SubjectRe: detecting integer constant expressions in macros
Date


talking of crazy ideas, here is another way to preserve
integer const expressions in macros by storing it a
VLA type (only for positive integers I guess):


#define MAX(a, b) sizeof(*({    \
        typedef char _Ta[a];    \
        typedef char _Tb[b];    \
        (char(*)[sizeof(_Ta) > sizeof(_Tb) ? sizeof(_Ta) :
sizeof(_Tb)])0; }))

Am Dienstag, den 20.03.2018, 23:13 +0100 schrieb Martin Uecker:
> Hi Linus,
>
> here is an idea:
>
> a test for integer constant expressions which returns an
> integer constant expression itself which should be suitable
> for passing to __builtin_choose_expr might be:
>
> #define ICE_P(x) (sizeof(int) == sizeof(*(1 ? ((void*)((x) * 0l)) :
> (int*)1)))
>
> This also does not evaluate x itself on gcc although this is
> not guaranteed by the standard. (And I haven't tried any older
> gcc.)
>
> Best,
> Martin
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