The third option is to chunk the input and convert each chunk independently. Ideal input chunks would be 8 bytes or fewer, because nearly all environments will support a uint64 type and nearly all hardware can do a divmod on them. If you're using base-10 then there's going to be a function that can “print” a uint64 to digits for you, so let's take digits as an example. With a chunk size of two bytes you would get five digits. Each digit takes 3⅓ bits of space, so 16 input bits takes 16⅔ bits: 96% efficient. Less than the 99.66% we can get with digits for sure. But if you consider all chunk sizes from one to eight bytes, turning 7-byte chunks into 17 digits is 98.82% efficient. That's pretty good for the complexity savings.