https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989
--- Comment #28 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 28 Oct 2022, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989 > > --- Comment #27 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > (In reply to Richard Biener from comment #26) > > Does the C standard limit the number of bits? Does it allow > > implementation defined limits? > > The latter. limits.h defines BITINT_MAXWIDTH, which must be at least as large > as number of bits in unsigned long long. AFAIK LLVM plans 8388608 maximum > (but > due to the missing library support uses 128 as maximum right now). > > > Constants are tricky indeed but I suppose there's no way to write a > > 199 bit integer constant in source? We can always resort to constants > > of the intfast_t[n] representation (aka a CTOR). > > One can specify even very large constants in the source. > 123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789uwb > will be _BitInt with the minimum number of bits to store the above unsigned > constant. > > > That said, if C allows us to limit to 128bits then let's do that for now. > > 32bit targets will still see all the complication when we give that a stab. > > I'm afraid once we define BITINT_MAXWIDTH, it will become part of the ABI, so > we can't increase it afterwards. Quite likely yes (OTOH __BIGGEST_ALIGNMENT__ changed as well). That also means BITINT_MAXWIDTH should eventually be decided by the ABI groups? I also can hardly see any use for very big N other than "oh, cool". I mean, we don't have _Float(N) either for N == 65000 even though what would be cool as well. > Anyway, I'm afraid we probably don't have enough time to implement this > properly in stage1, so might need to target GCC 14 with it. Unless somebody > spends on it > the remaining 2 weeks full time. It's absolutely a GCC 14 task given the ABI and library issue.
