Re: Efficient Matrix?

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

Robert A Duff <bobduff@shell01.TheWorld.com> wrote:

> Compilers are required to pack tightly in this case (one bit per Boolean
> component).  I.e., Matrix'Component_Size will be 1 if there's a pragma
> Pack.  See RM-13.2(9).

Hmm?

with Ada.Text_IO; use Ada.Text_IO;

procedure bla is

   type MATRIX is array (Positive range <>, Positive range <>) of Boolean;
   type POINTER_MATRIX is access all MATRIX;

   pragma Pack (MATRIX);

   type my_matrix is array (Positive range <>, Positive range <>) of Boolean;

   A : POINTER_MATRIX := new MATRIX (1 .. 10000, 1 .. 5000);

begin
   Put_Line (Integer'Image (MATRIX'Component_Size));
   Put_Line (Integer'Image (my_matrix'Component_Size));
end bla;


adi@drcomp:/tmp$ ./bla
 8
 8
adi@drcomp:/tmp$
 
> 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.


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