Useful discussion on Stack Overflow: https://stackoverflow.com/questions/16198700/using-the-extra-16-bits-in-64-bit-pointers https://stackoverflow.com/questions

Useful discussion on Stack Overflow: https://stackoverflow.com/questions/16198700/using-the-extra-16-bits-in-64-bit-pointers https://stackoverflow.com/questions/16198700/using-the-extra... Upshot: you can probably get away with it if you are careful to canonicalize pointers before using them.