[m-users.] Too Slow

[Matthias Güdemann]

Hi Peter,

thank you for your comments, I integrated them with the exception of
two:

> Most foreign procs could be more succinctly written, e.g.

> :- pragma foreign_proc("C", mp_init(Value::in, Result::out,
>                                     Mp_Int::out),
>   [will_not_call_mercury, promise_pure, thread_safe],
>   "
>    Mp_Int = MR_GC_NEW_ATTRIB(mp_int, MR_ALLOC_ID);
>    Result = mp_init(Mp_Int);
>    if (Result == MP_OKAY) {
>      Result = mp_set_int(Mp_Int, Value);
>      }
> ").

I fully agree with you, but I think the C compiler will do that
anyway. As "--no-c-optimize" must be specified explicitly, I assume
that at least some optimization will be done normally, and the
superfluous ints will go away.

,----
| to_int(A, N) :-
|     ( ( A >= min_int, A =< max_int) ->
|         mp_to_long(A, N)
|     ;
|         fail
|     ).
|
| :- pred mp_to_long(mp_int::in, int::out)
|     is det.
| :- pragma foreign_proc("C",
|                       mp_to_long(A::in, N::out),
|                       [will_not_call_mercury, promise_pure, thread_safe],
| "
|   unsigned long n;
|   n = mp_get_long(A);
|   N = (int) n;
| ").
`----

> Hmm.

The predicate checks whether the value is between min and max int,
shouldn't this therefore work? (I added the explicit cast to int at the
end).

> It would be preferable to statically allocate the mp_ints for these
> values.  Something like:

>     :- pragma foreign_decl("C", local, " static mp_int constant_one;
> ...  ").

>     :- initialise init/2.

>     :- pred init(io::di, io::uo) is det.

>     init(!IO) :- ...

>     :- pragma foreign_proc("C", one = (X::out), [ ... ], " X =
> &constant_one; ").

> But it can be left for later.

this is not done yet. Could this not simply be memoized?

Best regards,
Matthias