From owner-freebsd-questions@FreeBSD.ORG  Fri Dec  3 08:53:07 2004
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 704FC16A4CE
	for <freebsd-questions@freebsd.org>;
	Fri,  3 Dec 2004 08:53:07 +0000 (GMT)
Received: from mr.tuwien.ac.at (mr2-n.kom.tuwien.ac.at [128.131.2.110])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 7D71D43D46
	for <freebsd-questions@freebsd.org>;
	Fri,  3 Dec 2004 08:53:06 +0000 (GMT)
	(envelope-from e0025265@student.tuwien.ac.at)
Received: from webmail.zserv.tuwien.ac.at (lps.ben.tuwien.ac.at
	[193.170.74.11])
	by mr.tuwien.ac.at (8.12.10/8.12.8) with SMTP id iB38r2Ew014151
	for <freebsd-questions@freebsd.org>;
	Fri, 3 Dec 2004 09:53:03 +0100 (MET)
MIME-Version: 1.0
X-Mailer: V-webmail 1.5.1 ( http://www.v-webmail.co.uk/ )
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-ID: <i8520e.z7poi7@webmail.tuwien.ac.at>
Date: Fri,  3 Dec 2004 09:53:02 +0100
From: "Florian Hengstberger" <e0025265@student.tuwien.ac.at>
To: FreeBSD mailinglist <freebsd-questions@freebsd.org>
X-Vwebmail-Auth: e0025265@stud3.tuwien.ac.at
X-Virus-Scanned: by amavisd-milter (http://amavis.org/)
Subject: Floating Point Arithmetic
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>,
	<mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>,
	<mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 03 Dec 2004 08:53:07 -0000

Hi!

I tried to figure out the capability of double:
so I calculated 

d=2**n (with a for-loop)

increasing n step by step.
Of course I get a floating point exception when
d is bigger than 10**308.
But what makes me wondering is the fact that printing
printf("%lf",d) gives me the full range of numbers!

Calculating 2**1000 and I got the correct number
with all (!!) digits. (I cross-checked the digits with python.)
This is unexpected because sizeof(double) on my machine is 8,
and so I thought that the limit for the correct representation
is 2**(8*8).
(Actually the limit should be - meeting the IEEE standard -
2**52, the space reserved for representing the fraction of
a floating point number.) 
Anyway I can calculate 2**n, with n up to 1023 exact.
Why is this???

Thanks
Florian

PS: I even had a look at the assembly code, for printf
the %lf and than twice 32bit a pushed on the stack before
calling printf. Still not enough memory to represent 2**1000!