I have values that are 64-bit unsigned ints, and I need to store them in mongodb, which has no unsigned int type. I see three main possibilities for storing them in other field types, and converting on going in and out:

Using a signed int is probably easiest and most space efficient, but has the disadvantage that they're not human readable and if someone forgets to do the conversion, some of them will work, which may obscure errors.

Raw binary is probably most difficult for inexperienced programmers to deal with, and also suffers from non-human-readability.

A string representation is the least space efficient (~40 bytes in unicode vs 8 bytes per field), but then at least all of the possible values will map properly, and for querying only a conversion to string is required instead of a more complicated conversion.

I need these values to be available from different platforms, so a single driver-specific solution isn't an option.

Any major pros and cons I've missed? Which one would you use?