Re: Iteratively calling Prolog from C

[Lindsey Spratt]

On Thursday, July 17, 2003, at 10:15  AM, Daniel Dudley wrote:
> It would appear that gprolog does have something seriously
> wrong with its implementation. :-(
>
>     Win-Prolog 4.320           ECLiPsE 5.6
>     (no big number library)    (has big number library)
>     -----------------------    ------------------------
>     ?- factorial(17,F).        ?- factorial(17, F).
>     F = 355687428096000        F = 355687428096000
>                                Yes (0.00s cpu)
>
>     ?- factorial(18,F).        ?- factorial(18, F).
>     F = 6.402373705728E015     F = 6402373705728000
>                                Yes (0.00s cpu)
>
>     GNU Prolog
>     ----------
>     ?- factorial(17,F).
>     F = 248348672
>     yes
>
>     ?- factorial(18,F).
>     F = 175308800
>     yes

This is an integer/float issue. If you force all of the factorial 
calculations to be done using floats, then you get the right answers in 
gprolog.

factorial(N, F) :-
        FN is float(N),
        factorial(FN, 1.0, F).


factorial(1.0, N, N) :- !.

factorial(N, J, F) :-
        N > 1,
        K is N - 1.0,
        L is N * J,
        factorial(K, L, F).

?- factorial(17, F)
Success
F = 355687428096000.0

Lindsey Spratt
http://homepage.mac.com/lspratt