The constexpr didn't compile with Clang.  Changed to just inline the function.
The constexpr didn't compile with Clang.  Changed to just inline the function.

amichaelt/BDSup2SubPlusPlus,darealshinji/BDSup2SubPlusPlus,darealshinji/BDSup2SubPlusPlus,amichaelt/BDSup2SubPlusPlus