Re: conversions between fixed-point types

[sjw <simon.j.wright@mac.com>]

On Sep 20, 7:55 pm, Dirk Herrmann <fight_s...@invalid.invalid> wrote:

> As I said when I started this thread, I am currently investigating whether Ada
> could be a good replacement for the proprietary fixed-point oriented language
> used in our company.  And, convincing my colleagues would certainly not be
> easier with statements like "Ada can be used, but you have to implement all
> fixed-point stuff yourself".  Even more if you can not even rely on the fact
> that a compiler will behave the same way throughout.

Is the target hardware standard? (eg, PPC without floating-point
support) If not, you're looking at a compiler port as well.

Even though GNAT/x86 seems to truncate on predefined operations and on
conversion from static values (though not, as far as I can tell, on
dynamic conversion between two types!), there seems no intrinsic
reason why a port to different hardware might not be made to round.

> Robert A Duff wrote:

> > By the way, you can say:
>
> >     for T'Small use T'Delta;
>
> > to avoid repeating yourself.
>
> I have tried that, especially since the very same recommendation was given in
> the Barnes book "Ada 2005".  But, GNAT gives an error message.  It seems that
> the very moment you reference T'Delta the type T gets "frozen" such that  the
> "use" statement itself freezes T before it can modify it.  I don't know if
> this is what the authors of the reference manual had intended, but GNAT
> interprets it that way.

The idiom used to the

T_Delta : constant := 0.4;
type T is delta T_Delta range -10.0 .. 10.0;
for T'Small use T_Delta;