Re: Bitmanipulation in Ada

[Bernd.Specht@gmx.com (Bernd Specht)]

"Ed Falis" <falis@verizon.net> wrote in news:opscx5geap5afhvo@localhost:

> On 18 Aug 2004 21:10:30 GMT, Bernd Specht <Bernd.Specht@gmx.com> wrote:
> 
>> OK, but this would result in an assignment operation (a memory move on
>> maschine code level). What I want is a real "overlay" (same storage  
>> location used for both), so reading the value would not need extra
>> instructions. 
> 
> In all implementations of which I'm aware (and I've been in the Ada  
> compiler business for over 20 years) no code would be generated for an  
> unchecked conversion where the source and target have the same size.

Sorry, but that's absolutely *nonsense*

Have a look at Ludovics code:

with Ada.Unchecked_Conversion;
procedure P is
   type Byte_Array is array (1 .. Integer'Size) of Boolean;
   pragma Pack (Byte_Array);
   for Byte_Array'Size use Integer'Size;
   function To_Byte_Array is new
      Ada.Unchecked_Conversion (Source => Integer, Target => Byte_Array);
   I : Integer := 42;
   B : Byte_Array := To_Byte_Array (I);
begin
   null;
end P;


You agree that "I" and "B" are located at different adresses? Do you 
*really* think that you need *no* code to move data from one address to 
another??? That's wrong! You need at least *one* instruction, and this can 
be time consuming - especially if the data is missaligned and/or the code 
runs in a multiprocessor environment.


> You sound like you're looking for things to complain about, by the way.

Sorry - but you seem to be a blatherer.


>  (and I've been in the Ada compiler business for over 20 years) 

Wow! Be happy.


> 
> - Ed

*plonk*