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FIXNUM considered unportable
- To: mitccc!common-lisp%SU-AI%mc@angel.ARPA
- Subject: FIXNUM considered unportable
- From: George Carrette <lmi-angel!gjc%LMI-ANGEL.ARPA>
- Date: Fri, 25 Jul 1986 18:39:00 -0000
What all this discussion says to me as a compiler implementor is that
I should give a warning when somebody uses type FIXNUM.
Ah, but show now I can think of a use of type FIXNUM from MACSYMA
(DOE-MACSYMA, CL-MACSYMA whatever), and it seems quite reasonable.
Given that we know that fixnum operations are more efficient than non-fixnum
we choose to do our math modulo various prime numbers that fit in a fixnum.
Macsyma has a list of the 10 or so bigest primes that fit in a fixnum for
each machine it runs on, and/or it can compute these on the fly, using the
(LSH -1 -1) idiom (or other more common-lisp ways of finding the greatest fixnum).
Well, thats part of the justification, the code would look something like:
(COND ((TYPEP *MODULUS* 'FIXNUM)
(DECLARE (FIXNUM *MODULUS*))
....frob... frob... frob...))
..... frob ... frob ...))