bear wrote:
> For example, if I know that I added something to 27 and got -32,
> reversibility means I should be able to uniquely determine what was
> added to 27; under the rules of linear addition, it would have to be
> -59, not any positive number.  But with modular addition, it could be
> either of two numbers, -59 and ($MODULUS - 59), so modular addition
> isn't reversible like linear additon.

Yeah, but if you have the additional information that all "numbers" are
in the range -2^31 to 2^31-1 inclusive, you can determine the unique
value that was added to 27 to give -59.

I'm not saying fixnums are great, just that your example doesn't
convince me that addition of fixnums is not reversible.

Regards,

Alan
--
Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México