Re: Addressing in Object Ada v/s GNAT (2013) showing Vast Differences

[Lucas Redding <lucas.redding@gmail.com>]

On Monday, September 21, 2015 at 2:52:10 PM UTC+1, Georg Bauhaus wrote:
> On 21.09.15 15:22, Lucas Redding wrote:
> > On Monday, September 21, 2015 at 12:57:09 PM UTC+1, Jacob Sparre Andersen wrote:
> >> Lucas Redding wrote:
> >>
> >> Your examples don't compile.  Please show us the actual code.
> >>
> >> Greetings,
> >>
> >> Jacob
> >> --
> >> "Very small. Go to sleep" - monster (not drooling)
> >
> > Hi Jacob
> >
> > thanks for that. I am avoiding having to flood this with tons of code. So here is a compiled example.
> >
> > package interface_p
> > is
>   (...)
> > end INTERFACE_P ;
> >
> 
> Is this happening only when you read from the shared location?
> I see the output
> local a:     1, local b:     2
> from the following program, compiled using GNAT GPL 2014 on a Mac:
> 
> With Ada.Text_IO;
> with INTERFACE_P; use INTERFACE_P;
> procedure Test_Interface_P
> is
>     It : local_rec;
> begin
>     It := READ_RECORD;
>     
>     declare
>        use Ada;
>        package Xintio is new Text_IO.Integer_IO (sixteen_bits);
>     begin
>        Text_Io.Put ("local a:"); Xintio.Put (It.a);
>        Text_Io.Put (", local b:"); Xintio.Put (It.b);
>        Text_Io.New_Line;
>     end;
> 
> end Test_Interface_P;

Totally agree. Both you and Jacob are correct.

There must be something subtle in my definitions that I am missing.

Note the new code below which reflects the real code except the array of bytes is much larger. I hall keep digging and report back.

Thank you very much.

with SYSTEM ;
package mapping 
is

   type thirty_two_bits is range 0..(2**31)-1;
   for thirty_two_bits'size use 32 ;
   for thirty_two_bits'Alignment use 1 ;
   
   type byte_t is range 0..255 ;
   for byte_t'size use 8 ;
   for byte_t'alignment use 1 ;
   
   type byte_stream is array (0..3) of byte_t ;
   for byte_stream'Component_Size use 8 ;
   for byte_stream'Alignment use 1;
   
   MAPPED_ARRAY : byte_stream := ( 16#01#, 16#80#,16#0#, 16#0# ) ; 
   
   MAPPED_ITEM : thirty_two_bits  ;
   for MAPPED_ITEM use at MAPPED_ARRAY'Address ; 
   MAPPED_ITEM_ADDRESS : System.Address := MAPPED_ITEM'Address ;

end mapping ;

with mapping ;

package interface_p
is

   type thirty_two_bits is range 0..(2**31)-1;
   for thirty_two_bits'size use 32 ;
   for thirty_two_bits'Alignment use 1 ;

   type sixteen_bits is range 0..(2**16)-1 ;
   type fourteen_bits is range 0..(2**14)-1;
   type ten_bits is range 0..(2**10)-1;
   type padding_bits is range 0..(2**8)-1 ;

   type rec is record
      a: fourteen_bits ;
      b: ten_bits ;
      padding : padding_bits ;
   end record ;

   for rec use
   record
      a at 0 range 0..13 ;
      b at 0 range 14..23 ;
      padding at 0 range 24..31;
   end record ;
   for rec'size use 32;
   for rec'alignment use 1;

   subtype local_fourteen_bits is sixteen_bits range 0 .. (2 ** 14)-1;
   subtype local_ten_bits is sixteen_bits range 0 .. (2 ** 10)-1;
   type local_rec is record
      a : local_fourteen_bits ;
      b : local_ten_bits ;
   end record;

   for local_rec use
   record
      a at 0 range 0 .. 13 ;
      b at 2 range 0 .. 9 ;
   end record;

   for local_rec'size use 32 ;
   for local_rec'Alignment use 1 ;
   
   MAPPED_ITEM : thirty_two_bits ;
   for MAPPED_ITEM'Address use mapping.MAPPED_ITEM_ADDRESS ;

   VAR_REC : rec ;
   for VAR_REC use at MAPPED_ITEM'Address ; 

   -- I explicitly assign here but in actual application it maps onto a 32 bit
   -- record in memory. I have deliberately changed in order to avoid adding
   -- tons of irrelevant code.


   function READ_RECORD
   return local_rec ;

end interface_p ;


In the system, the mapping is to an array of bytes populated in memory and then mapped.