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-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news2.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!newsfeed00.sul.t-online.de!t-online.de!news.albasani.net!not-for-mail
From: Dirk Herrmann <fight_spam@invalid.invalid>
Newsgroups: comp.lang.ada
Subject: Re: conversions between fixed-point types
Date: Sun, 20 Sep 2009 10:15:49 +0200
Organization: albasani.net
Message-ID: <h94obl$c7h$1@news.albasani.net>
References: <h90uf3$bdo$2@news.albasani.net> <h92jie$q4g$1@news.albasani.net>
 <nospam-3D5AA1.10481219092009@news.aioe.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: news.albasani.net
 zrVNeXP9guJTljp+65mrV7h4Uro7vVuE7KHu5LO7hi/xuYWdDPOBT9FFvstmVfPSMS44+xd72ST+mfpKeRUeRgFNNznwKPYloW1wpOuJ4+J87Q/hQCz5lzHzG00j35E4
X-Complaints-To: abuse@albasani.net
NNTP-Posting-Date: Sun, 20 Sep 2009 08:15:49 +0000 (UTC)
X-User-ID: 
 De7O6/rVRuXhk5qNrXEmRT5Em0JQQUFmUYjnSQ13ztTRqut9S4QmMah7Sg4HK2LjvSdJYL2995PKatQhOYrUeQ==
In-Reply-To: <nospam-3D5AA1.10481219092009@news.aioe.org>
Cancel-Lock: sha1:3pLsEBF7zcJP4RD2deHOyzcfz/U=
User-Agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090706)
X-NNTP-Posting-Host: p3pG0j44w36ctcwibm/vGEqE1XXtInH0Cb7F74td8lo=
Xref: g2news2.google.com comp.lang.ada:8401
Date: 2009-09-20T10:15:49+02:00
List-Id: <comp.lang.ada>

Dirk Herrmann wrote:
>> And, while experimenting and trying out Adam Beneschan's solution for 
>> rounding (thanks for your answer, Alan) I got totally confused 
>> because of the following code (I am using GNAT 4.3.4 with the 
>> following command line options: gnatmake -f -gnatVa -gnata 
>> -gnatwadhl.o -save-temps conversion.adb):
> [...]
>> Is this confusing behaviour allowed?  I will submit a bug report if 
>> some expert confirms it is a GNAT bug.

John B. Matthews wrote:
> I'm no expert, and I had some trouble following the conversions in your 
> example.  [...]

Sorry, I should have given more details about why I am confused.

In particular I am disturbed by the fact that the following two lines produce 
different results with GNAT, as has been confirmed for GNAT 3.15p (thanks, 
tmoran):
       FIO.Put(Float(FpB(Float(-1.5)))); TIO.Put(" ");      --> -1.20000E+00
       FIO.Put(Float(MakeB(-1.5))); TIO.Put(" ");           --> -1.60000E+00
In the first line, the conversion to FpB is done from a Float value, which is 
a direct cast from -1.5.  In the second line, the conversion to FpB is also 
done from a Float value, but in this case -1.5 is passed as a Float argument 
to MakeB.  What I don't understand is, why it should make a difference whether 
I cast -1.5 to Float and then convert it to FpB compared to the situation 
where -1.5 is converted to a Float argument, which is then converted to FpB.

The same question arises for the following three lines:
       FIO.Put(Float(FpB(FpA(Float(-1.5))))); TIO.Put(" "); --> -1.20000E+00
       FIO.Put(Float(MakeBFromA(FpA(-1.5)))); TIO.Put(" "); --> -1.60000E+00
       FIO.Put(Float(MakeBViaA(-1.5))); TIO.Put(" ");       --> -1.60000E+00
Again, the difference lies in whether a sequence of casts is used compared to 
whether the very same value is passed as an argument.

Thanks for your help,

Dirk Herrmann
(email address gladly given on request)