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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Side-effect arithmetic again [was: Ada ... in embedded systems]
Date: 1996/03/21
Message-ID: <EACHUS.96Mar21184540@spectre.mitre.org>#1/1
X-Deja-AN: 143660464
distribution: world
references: <4hv2fb$6ra@cville-srv.wam.umd.edu>
 <4il3ce$fqa@saba.info.ucla.edu>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-03-21T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <4iq2ia$lk7@dayuc.dayton.saic.com> John G. Volan <John_Volan@ccmail.dayton.saic.com> writes:

  > I wasn't throwing down a gauntlet or anything, just throwing out an idea 
  > for consideration ... :-)

   But since you took the gauntlet back, I'll suggest some of the
things I was going to put in:

  > No need to think about it overnight, _both_ can be done fairly
  > trivially:
 
  (My conclusion was that you really only need one package:)

  ------------------------------------------------------------------------
  generic
    type Item is (<>);
  package Discrete_Arithmetic is

    procedure Increment (This : in out Item);

    procedure Decrement (This : in out Item);

    --add

    procedure Increment (This : in out Item; By: in Positive);
    procedure Decrement (This : in out Item; By: in Positive);

    procedure Cycle (This: in out Item);

    --moved for obvious reasons.

    pragma Inline (Increment);
    pragma Inline (Decrement);
    pragma Inline (Cycle);

  end Discrete_Arithmetic;
  ------------------------------------------------------------------------
  package body Discrete_Arithmetic is

    procedure Increment (This : in out Item) is
    begin
      This := Item'Succ (This);
    end Increment;

    procedure Decrement (This : in out Item) is
    begin
      This := Item'Pred (This);
    end Decrement;

    procedure Increment (This : in out Item; By: in Positive) is
    begin
      This := Item'Val(Item'Pos(This) + By);
    end Increment;

    procedure Decrement (This : in out Item; By: in Positive) is
    begin
      This := Item'Val(Item'Pos(This) - By);
    end Decrement;

    procedure Cycle (This: in out Item) is
    begin
      if This = Item'LAST
      then This := Item'First;
      else This := Item'Succ(This);
      end if;
    end Cycle;
    
  end Discrete_Arithmetic;

  ------------------------------------------------------------------
--

					Robert I. Eachus

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