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=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,c6acbb9f2027b8c9
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!newspeer1.nwr.nac.net!colt.net!peernews3.colt.net!newsfeed.stueberl.de!npeer.de.kpn-eurorings.net!newsfeed.arcor.de!news.arcor.de!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: volatile vs aliased
Newsgroups: comp.lang.ada
User-Agent: 40tude_Dialog/2.0.14.1
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Reply-To: mailbox@dmitry-kazakov.de
Organization: cbb software GmbH
References: <1128525722.605730.281980@g43g2000cwa.googlegroups.com>
 <87mzlnomca.fsf@ludovic-brenta.org> <1421562.dbAHjS9XJS@linux1.krischik.com>
Date: Thu, 6 Oct 2005 10:52:59 +0200
Message-ID: <axg1qv1ymzpy$.1khzy65odwd71.dlg@40tude.net>
NNTP-Posting-Date: 06 Oct 2005 10:52:59 MEST
NNTP-Posting-Host: c1c5b081.newsread2.arcor-online.net
X-Trace: 
 DXC=D8@RGiV<n_jd:IG0JE`:@gQ5U85hF6f;djW\KbG]kaMhGSi?jHD8GO`on\\O]B`]En[6LHn;2LCVn7enW;^6ZC`d<=9bOTW=MNn
X-Complaints-To: abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:5437
Date: 2005-10-06T10:52:59+02:00
List-Id: <comp.lang.ada>

On Thu, 06 Oct 2005 10:05:38 +0200, Martin Krischik wrote:

> Ludovic Brenta wrote:
> 
>> pragma Volatile (Variable) says the compiler must not optimise away
>> any reads or writes to that variable, and that it may not add extra
>> reads or writes beyond those you explicitly request in your program
>> text.  You want to use that for hardware registers, where a "read"
>> operation may have a side effect such as changing the device's state.
> 
> Interesting! So with  pragma Volatile (X) the following two statements are
> not the same:
> 
> Y := X * X;
> Y := X ** 2;
>
> Good to know!

BTW, even without Volatile, they are not necessary same!

For intervals X*X /= X**2!

Example:

[-1, 2] * [-1, 2] = [-1, 4]

[-1, 2]**2 = [2, 4]

X**2 is as twice as more accurate than X*X.

To improve accuracy of * and /, arguments need to be analyzed for
dependency. X + X = 2 * X, no matter what.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de