This is also a common technique used by modern Javascript implementations. A much less common and slightly more interesting approach (to me) is NaN boxing - tha

This is also a common technique used by modern Javascript implementations. A much less common and slightly more interesting approach (to me) is NaN boxing - that packs tags into unused NaN bit ranges of doubles that are encoded per the IEEE-754 format. Chakra uses the bottom most bit to distinguish SMIs from pointers.