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: 103376,91965a012526b259
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news1.google.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Float to String
Date: Tue, 9 Nov 2004 09:39:42 +0100
Message-ID: <526nxsbun7e2.1n5a4jpe7u7ww$.dlg@40tude.net>
References: <uekj4l18j.fsf@obry.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Trace: news.uni-berlin.de IDCY55zuAL5mhlquYn4VawX5BgQLdEpV7vYG4nVVT+8AZSBpQ=
User-Agent: 40tude_Dialog/2.0.12.1
Xref: g2news1.google.com comp.lang.ada:6072
Date: 2004-11-09T09:39:42+01:00
List-Id: <comp.lang.ada>

On 08 Nov 2004 18:06:04 +0100, Pascal Obry wrote:

> I was wondering if there is a way to save a float into a string and read it
> back without loosing precision ?
> 
> I tried something like:
> 
>    F_Str : String (1 .. Float'Base'Digits);
> 
>    Float_Text_IO.Put (F_Str, My_Float, Aft => Float'Base'Digits);
> 
> But this is not enough... Ideas ?

There is no any portable way to do so. Floating-point numbers are intended
to be imprecise. Normally the application domain should determine the
required accuracy. It is definitely possible to maintain that accuracy
during I/O conversions. What is impossible and meaningless, is to try to
define the *application-specific* accuracy as "the ultimate accuracy of
Float on this concrete machine for this concrete compiler". Another
question is asymptotic behavior of repeated forth and back conversions. I
would not expect that its error is unbounded, however ARM is silent about
that.

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