[racket] 80-bit precision in Racket

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Fri Nov 9 11:40:17 EST 2012

At Fri, 09 Nov 2012 19:34:00 +0400, Dmitry Pavlov wrote:
> 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?

Unboxing is a collaboration between the JIT and the bytecode compiler.
There are various "value is known to be a flonum" flags that are
threaded through the compiler, bytecode, validator, and JIT. In some of
those places, there's room for an extra bit of information, but in
other places, we'll have to adjust representations to make room for
more bits.

I'll look into this more. It would be nice to have fixnum unboxing, and
maybe that would be a good experiment toward unboxing for other types
as well.

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