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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Saturated Math
Date: 30 May 2003 15:31:11 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2003-05-30T15:31:11-04:00
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"Randy Brukardt" <randy@rrsoftware.com> writes:

> Dale Stanbrough wrote in message ...
> >I don't like the idea that you have to create a dummy type...
> >
> >   type Pretend_Type is new Integer range 1..5;
> >   package Saturated_Int is new Saturate (Pretend_Type);
> >   ...
> >
> >It seems a bit clunky just to get around the type system. I
> >thought of passing in an upper and lower bound to the generic,
> >but what type should they be? You could make them integer, but
> >what if you wanted saturating integers with a larger range than
> >Standard.Integer?
> 
> 
> It's mildly annoying that Ada doesn't have a standard name for the
> largest range integer type supported by the implementation. (The
> standard defines Root_Integer, but it is not a name that you can use in
> a program.) But it is easy enough to declare:
> 
>     type Largest_Integer_Type is range System.Min_Int .. System.Max_Int;
> 
> The, the generic could look something like:
> 
>     generic
>         Lower_Bound, Upper_Bound : Largest_Integer_Type;
>     package Saturated_Math is
>        type Saturated_Type is Lower_Bound .. Upper_Bound;

But the bounds are not static expressions, as required, and you're
missing "range".  Or did you mean "subtype"?

>        function "+" (Left, Right : Saturated_Type) return
> Saturated_Type;
>        ...
>     end Saturated_Math;
> 
> Using this would be virtually the same as using predefined integer
> types. (We use something like this to emulate the target machine's math
> in the Janus/Ada compiler. Why do that? We needed it for the Unisys 2200
> compiler, as that is a one's complement, 36-bit machine.)
> 
>                   Randy.