https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106865
--- Comment #2 from cqwrteur <unlvsur at live dot com> ---
template<typename T>
inline constexpr T add_carry(T a,T b,T carryin,T& carryout) noexcept
{
a+=b;
carryout=a<b;
a+=carryin;
carryout+=a<carryin;
return a;
}
template<typename T>
inline constexpr T sub_carry(T a,T b,T carryin,T& carryout) noexcept
{
a-=b;
carryout=b<a;
a-=carryin;
carryout+=carryin<a;
return a;
}
https://godbolt.org/z/ETnzKxGGd
This pattern is even better. It generates identical code with clang's builtin.
The only problem is that it does not work on archs that provide carry flags.
