On Wed, Jul 24, 2024, at 13:59, Anshuman Khandual wrote: > On 7/24/24 16:33, Arnd Bergmann wrote: >> I would hope we don't need this definition. Not that it >> hurts at all, but __BITS_PER_LONG_LONG was already kind >> of pointless since we don't run on anything else and >> __BITS_PER_U128 clearly can't have any other sensible >> definition than a plain 128. > > Agreed, although this just followed __BITS_PER_LONG_LONG. > But sure __BITS_PER_U128 can be plain 128. > > So would you like to have #ifndef __BITS_PER_LONG_LONG dropped here > as well ? But should that be folded or in a separate patch ? A separate patch is probably better, but you can also just leave it. >>> #define __AC(X,Y) (X##Y) >>> #define _AC(X,Y) __AC(X,Y) >>> #define _AT(T,X) ((T)(X)) >>> +#define _AC128(X) ((unsigned __int128)(X)) >> >> I just tried using this syntax and it doesn't seem to do >> what you expected. gcc silently truncates the constant > > But numbers passed into _AC128() are smaller in the range [128..0]. > Hence the truncation might not be problematic in this context ? OR > could it be ? > >> to a 64-bit value here, while clang fails the build. > > Should this be disabled for CC_IS_CLANG ? > >> See also https://godbolt.org/z/rzEqra7nY >> https://stackoverflow.com/questions/63328802/unsigned-int128-literal-gcc > > So unless the value in there is beyond 64 bits, it should be good ? > OR am I missing something. > >> The __GENMASK_U128() macro however seems to work correctly >> since you start out with a smaller number and then shift >> it after the type conversion. > > _U128() never receives anything beyond [127..0] range. So then this > should be good ? Since you define _U128() right next to _ULL(), I would argue that it should have the corresponding behavior for any value that can fit into the type. Since that is currently not possible with gcc, I would prefer to not define it at all. However, I think you can just define a _BIT128() macro that behaves the same way as _BITULL() and define __GENMASK_U128() based on that. Maybe something like #define _BIT128(x) ((unsigned __int128)1 << (x)) #define __GENMASK_U128(h, l) (_BIT128((h) + 1)) - (_BIT128(l)) Arnd
