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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: unsigned type
Date: Sun, 28 Jun 2009 19:54:28 +0000 (UTC)
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Date: 2009-06-28T19:54:28+00:00
List-Id: <comp.lang.ada>

>I am trying to declare a type as unsigned using Ubuntu 9.04 GNAT
>compiler.  I know Ada does not have a type CARDINAL, but I thought it
>had a type Unsigned.

Ada's equivalent is Natural.  If
  Lowest : Natural := 0;
  Highest : Natural := Natural'last;
then
  Lowest  := Lowest-1;  -- will raise an exception
  Highest := Highest+1; -- ditto

(Note that Gnat by default is not a legal Ada compiler because it doesn't
check for and raise the exception.  You need a command line parameter
-gnato to make it act like Ada.)

The standard Ada package Interfaces has hardware-oriented types
Unsigned_8, Unsigned_16, etc but those are modular types so if
  Empty_Word : Interfaces.Unsigned_16 := 0;
  Full_Byte  : Interfaces.Unsigned_8 := 255;
then
  Empty_Word-1 will be 65535.
  Full_Byte+1 will be 0.
with no exceptions raised.

You can also declare your own application oriented non-negative types
  type Ratings is range 1 .. 10;
or modular types
  type Degrees is mod 360;  -- 0 .. 359 wrapping around