Re: Memory limits in Ada where Fortran has none

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk> writes:

> On Sun, 06 Mar 2005 19:05:21 -0500, Robert A Duff wrote:
> 
> > The following works for me:
> > 
> > package Test_Pkg is
> >     X: array (1..400_000_000) of Integer := (others => 999);
> > end Test_Pkg;
> > 
> > with Test_Pkg; use Test_Pkg;
> > with Text_IO; use Text_IO;
> > procedure Test is
> > begin
> >     Put_Line(Integer'Image(X(X'Last)));
> > end Test;
> 
> I am very wary of a test like this because GNAT sometimes
> silently accesses the wrong element of very large data, if I
> remember correctly.

Well, the original poster was complaining that you can't allocate large
amounts of memory in Ada, but you can in Fortran, and I was just trying
to test that.  But, OK, how about this:

package Test_Pkg is
    pragma Elaborate_Body;
    X: array (1..400_000_000) of Integer := (others => 999);
end Test_Pkg;

package body Test_Pkg is
begin
    for I in X'Range loop
        X(I) := Integer'Last - I;
    end loop;
end Test_Pkg;

with Test_Pkg; use Test_Pkg;
with Text_IO; use Text_IO;
procedure Test is
begin
    for I in X'Range loop
        pragma Assert(X(I) = Integer'Last - I); null;
    end loop;
    Put_Line(Integer'Image(X(X'Last)));
end Test;

Works fine, for me.  Takes quite a while to run, of course,
since I don't have that much RAM on my machine.

>... A correctly written program can (and did!)
> thus fail catastrophically.  Large records in particular are
> suspect (on GNAT 3.15p, x86). (I have no test case to hand
> at the moment).  I don't know if it is affected by -gnato
> and default absence of overflow checking.

I guess you should send them a bug report.

> A more comforting test would place a *different* value at
> each location, and check they are all correct!

OK, the above example does that (but it's an array,
not a record).

- Bob