One comment in the article pointed out that you could create a 4GB lookup table, and convert 32 bits of input at once. This is actually less silly than might otherwise seem, because only 64KB of it would ever be read for correct input; the table itself would only exist as a reservation somewhere in the process' 64-bit (well, 48-bit actually, but still) virtual address space, so a lookup of invalid input could easily be made to error out and return some error condition.

For that matter, I'd want to run the author's "fancy math-based function" through a superoptimizer and check that there isn't something that can do the job in fewer cycles.