MdB says:
dividing by 2 is actually optimal. It's type correct for all usage, and the compiler generates the multiplication if it's float, and sticks with divide for integers
Godbolt indicates on any optimization level (O1-O3, and Os) that the compiler will correctly optimize the / 2 into a float multiplication if using a float, but if using integer types in the template it will stick with the / 2 which is faster then doing the conversions to/from float.
Andrew Tridgell
Peter Barker
Andrey Kolobov