[libcxx-commits] [PATCH] D102328: [libc++] Fix constraint for [bit.pow.two] functions

Arthur O'Dwyer via Phabricator via libcxx-commits libcxx-commits at lists.llvm.org
Wed May 12 10:24:39 PDT 2021

Quuxplusone added inline comments.

Comment at: libcxx/include/bit:89
         _IsNotSame<typename remove_cv<_Tp>::type, char16_t>::value &&
         _IsNotSame<typename remove_cv<_Tp>::type, char32_t>::value
jwakely wrote:
> Quuxplusone wrote:
> > Seems like we should add `char8_t` while we're here, yeah? (It is also integral and unsigned but not an unsigned integer type.)  For bonus clarity, we could make a type trait `__is_integer_type<_Tp>` and then this whole constraint on line 97 would be simply
> > ```
> > static_assert(__is_integer_type<_Tp>::value && is_unsigned<_Tp>::value, "__rotl requires an unsigned integer type");
> > ```
> > ...except that a static_assert is not a "constraint," so we're just totally nonconforming here.
> > @jwakely, thoughts? I'd volunteer to commandeer if you like.
> Yes, that should be there too. Feel free to take this, I only submitted it here because it seemed better to put the patch here than in bugzilla.
@mclow.lists, @ldionne: libc++ currently supports `__uint128_t` for these functions; do we want to keep supporting it?
libstdc++ does not support it: https://godbolt.org/z/jK9q8z6oT

I'm going to operate on the assumption that we want to keep it (as a non-conforming extension)...

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