Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Martin <martin.dowie@btopenworld.com>]

On Jan 16, 5:08 pm, ChristopherL <clusard...@aol.com> wrote:
> On Jan 16, 7:11 am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>
> >    type Signed_8 is range - 2**7 .. 2**7 - 1;
> >    for Signed_8'Size use 8;
>
> I didn't use the second line in my program! Without it, my system
> uses 10 bits for this. I'm going to use my solution for now.
>
> Also experimenting on my own, if I only make the below change the
> variable Result has a value of -62 and not as above (-56).
>
> --  type Short_integer1 is range 0.. ((2 ** 8) - 1);
> --  for Short_Integer1'Size use 8;
>
>   type Short_integer1 is mod 2 ** 8;
>   for Short_Integer1'Size use 8;
>
> What does the following line of code do? It's new to me and have to
> know!
>
> type Short_integer1 is mod 2 ** 8;
>
> Chris L.

"mod" indicates a 'modular' type - i.e. unsigned, with wrap-round
semantics (no exceptions). Analogous to C 'unsigned'. Useful for
masking - using 'and', 'or', etc.

If you want an unsigned 8-bit integer with those semantics, you can
use the predefined type Interfaces.Unsigned_8. The package
'Interfaces' name indicates that you are 'close to the metal' in some
why and you actually _care_ about the size of objects your
manipulating.

There is a very good Wikibook on Ada you know...

http://en.wikibooks.org/wiki/Ada_Programming

and in particular:

http://en.wikibooks.org/wiki/Ada_Programming/Types/mod

Cheers
-- Martin