Re: Bitmanipulation in Ada

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

Many thanks, this will help me a lot.


"Martin Dowie" <martin.dowie@btopenworld.com> wrote in
news:cg0j57$bal$1@sparta.btinternet.com: 

> Bernd Specht wrote:
>> 2. I did not found shift and rotate operations. Did I miss something
>> or are there really none? 
> 
> Check out package "Interfaces" they are all there - as are some common
> predefined types.
> 
>> 3. When I want treat a value both as an integer and as a boolean
>> array, how can i do this? In pascal I would use a tagless record like
> 
> Assuming you had a _really_ good reason to need to think of the data in
> both terms, you have a number of options:
> 
> 1) Unchecked_Conversion;
> 
> procedure Foo (Y : Unsigned_8) is
>    procedure To_Array_8 is
>       new Ada.Unchecked_Conversion (Unsigned_8, Array_8);
>    X : Array_8 := To_Array_8 (Y);
> begin
> ...
> 
> 2) Address clause to 'overlay' 2 variables at the same address;
> 
> procedure Foo (Y : Unsigned_8) is
>    X : Array_8;
>    for X'Address use Y'Address;
> begin
> ...
> 
> 3) Variant record with a representation clause;
> 
> type Variant (Is_Array : Boolean := False) is
> record
>    case Is_Array is
>       when False =>
>          U : Unsigned_8;
>       when True =>
>          A : Array_8;
>    end case;
> end record;
> for Variant use
> record
>    U at 0 range 0 .. 7;
>    A at 0 range 0 .. 7;
> end record;
> 
> This will leave it to the compiler where to put "Is_Array"
> 
> There are pros and cons to each - I'd rather use
> Ada.Unchecked_Conversion to make it explicit that I'm switching
> representations. 
> 
> Cheers
> 
> -- Martin
> 
>