From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: a07f3367d7,a97feceab5b57877
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII
Path: 
 g2news2.google.com!postnews.google.com!k30g2000yqf.googlegroups.com!not-for-mail
From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Saturation arithmetic woes.
Date: Thu, 30 Jul 2009 04:51:15 -0700 (PDT)
Organization: http://groups.google.com
Message-ID: 
 <b3bb887d-4428-400f-a420-5912910965db@k30g2000yqf.googlegroups.com>
References: 
 <1a16b458-0201-4320-9787-2836ed58f991@e27g2000yqm.googlegroups.com>
	<4a709faf$0$6282$4f793bc4@news.tdc.fi> <11or4h.tfh.ln@hunter.axlog.fr>
NNTP-Posting-Host: 20.133.0.8
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
X-Trace: posting.google.com 1248954675 1705 127.0.0.1 (30 Jul 2009 11:51:15
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Thu, 30 Jul 2009 11:51:15 +0000 (UTC)
Complaints-To: groups-abuse@google.com
Injection-Info: k30g2000yqf.googlegroups.com; posting-host=20.133.0.8;
	posting-account=g4n69woAAACHKbpceNrvOhHWViIbdQ9G
User-Agent: G2/1.0
X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.1.1)
	Gecko/20090715 Firefox/3.5.1,gzip(gfe),gzip(gfe)
Xref: g2news2.google.com comp.lang.ada:7444
Date: 2009-07-30T04:51:15-07:00
List-Id: <comp.lang.ada>

On Jul 30, 10:09=A0am, Jean-Pierre Rosen <ro...@adalog.fr> wrote:
> Niklas Holsti a =E9crit :
>
> >> package body Saturation is
>
> >> =A0 function "+"
> >> =A0 =A0 (Left =A0: Saturated_Type;
> >> =A0 =A0 =A0Right : Saturated_Type) return Saturated_Type
> >> =A0 is
> >> =A0 =A0 Temp_Left =A0: constant Discrete_Type :=3D Discrete_Type (Left=
);
> >> =A0 =A0 Temp_Right : constant Discrete_Type :=3D Discrete_Type (Right)=
;
> >> =A0 begin
> >> =A0 =A0 if Temp_Left + Temp_Right > Discrete_Type'Last then
>
> > Depending on the actual type associated with Discrete_Type (and assumin=
g
> > you use the predefined "+" for that type), you risk getting an overflow
> > on Temp_Left + Temp_Right. If you have overflow checks disabled (as Gna=
t
> > has by default) the sum may "wrap around" and seem to be less than
> > Discrete_Type'Last, giving you the wrong result. If you have overflow
> > checks enabled, you get a Constraint_Error instead of
> > Discrete_Type'Last. Ditto for underflow and Discrete_Type'First.
>
> But of course, the simplest way to check is to write:
> =A0 =A0if Temp_Left > Discrete_Type'Last - Temp_Right then
>
> No overflow, ever! Of course, you need a "-" operator, and I assume it
> is consistent with "+"...
> --
> ---------------------------------------------------------
> =A0 =A0 =A0 =A0 =A0 =A0J-P. Rosen (ro...@adalog.fr)
> Visit Adalog's web site athttp://www.adalog.fr

Temp_Right =3D -1 ?

Cheers
-- Martin