Messages in this thread | | | From | "Uecker, Martin" <> | Subject | Re: detecting integer constant expressions in macros | Date | Tue, 20 Mar 2018 23:07:28 +0000 |
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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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