[racket] 80-bit precision in Racket

Matthew,

 > Your plan sounds workable, but I wonder whether you'll want the JIT to
> unbox extnums in the same way that it unboxes flonums. That's not as
> easy as the rest of the plan, but generalizing Racket's unboxing
> machinery to deal with more types is something that we can consider.

Surely we will need the JIT to unbox extnums. Could you please tell
why it is harder than the rest of the plan? Ten bytes worse than
eight? Alignment issues?

Best regards,

Dmitry