bug / side effects?/ for fdiv?
Tue, 09 Sep 2003 00:03:35 -0700
I am using gmp 4.1 with common lisp bindings I set up for Allegro Common
Lisp, using foreign function interface.
.... i and q are gmp numbers...
(setf r (create_mpz_zero))
(mpz_fdiv_r_2exp r i logv) ;set r to remainder i by 2^logv
(mpz_fdiv_q_2exp q i logv) ;set q to quotient i by 2^logv
This works as expected. the call to mpz_fdiv_q is essentially a right
by logv bits.
However, if the div_r and div_q are reversed, then the remainder is
off by 1. This is repeatable, but doesn't happen on all inputs.
I know that this report is kind of sketchy, and I'm not supplying
you with the full context, (all is possible, but Allegro is not
open source etc etc etc).
I suspect this could be reproduced in any other language binding
i is 4611682719894601729, logv is 20.