Re: Efficient Matrix?

[Adrian Knoth <adi@drcomp.erfurt.thur.de>]

Bill Findlay <yaldnifw@blueyonder.co.uk> wrote:

>>> It's got nothing to do with the fact that the thing is heap allocated,
>>> nor the fact that the bounds are not known at compile time.
>> For the variable A it is even known, but I was not able to determine
>> a valuable difference in memory-comsumption.
> I get good results as follows, with GNAT 5.00w for MacOS X.

What you get is exactly what I meant:

The compiler optimizes if it is a constrained type and does nothing if
it is unconstrained as the original poster wanted it.

For sure it would be better to use a constrained subtype. Here your
program modified to the asked context:

with Ada.Text_IO; use Ada.Text_IO;

procedure bla is

   type unconstrained_type is
        array (Positive range <>, Positive range <>) of Boolean;
   for unconstrained_type'Component_Size use 1;
   pragma Pack (unconstrained_type);

   type unconstrained_type_ptr is access unconstrained_type;

   A : unconstrained_type_ptr := new unconstrained_type
                                      (1 .. 10000, 1 .. 5000);

begin
   Put_Line (Integer'Image (unconstrained_type'Component_Size));
   Put_Line (Integer'Image (A.all'Size));
end bla;

------
adi@drcomp:/tmp$ ./bla
 8
 400000000

(last value is 50000000*8)

-- 
mail: adi@thur.de  	http://adi.thur.de	PGP: v2-key via keyserver

Der merkt halt, dass das seine muttermilch ist, die gerade �bertragen wird.
(user w�hrend des dd's der root-partition auf den fileserver)