X-Spam-Check-By: sourceware.org Message-ID: <440AEE89.7050206@cs.unipr.it> Date: Sun, 05 Mar 2006 14:58:33 +0100 From: Roberto Bagnara User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050929 Thunderbird/1.0.7 Fedora/1.0.7-1.1.fc4 Mnenhy/0.7.3.0 MIME-Version: 1.0 To: skaller CC: tprince@computer.org, cygwin@cygwin.com, "The Parma Polyhedra Library developers' list" Subject: Re: Precision of doubles and stdio References: <4408B886.5010209@cs.unipr.it> <4408C140.9030100@myrealbox.com> <440ACF12.7000403@cs.unipr.it> <1141564216.10188.27.camel@budgie.wigram> In-Reply-To: <1141564216.10188.27.camel@budgie.wigram> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com skaller wrote: > On Sun, 2006-03-05 at 12:44 +0100, Roberto Bagnara wrote: >> Tim Prince wrote: >> My >>> past reading of various relevant documents convinced me that digits >>> beyond the 17th in formatting of doubles are not required by any >>> standard to be consistent between implementations. They have no useful >>> function, as 17 digits are sufficient to determine uniquely the >>> corresponding binary value in IEEE 754 format. >> Thank you Tim. We were unaware of this giant bug in the C standard. >> All the best, > > There is no bug in the C Standard. The C standard makes it > clear the accuracy of floating point operations is > implementation defined ,and the implementor may even say the > accuracy is undefined. Which operations are you talking about? I am not talking about floating point operations. > This is not a bug, it is the proper thing for a language > standard. Call it the way you want: I call `buggy' a standard that allows an invocation of printf("%.37g\n", d); to silently ignore 20 or so significant digits (and apparently for no good reason, by the way). You can call it `bad design', if you prefer. Or `unfortunate legacy'. You are of course free to call it `good design' if you like it. All the best, Roberto -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/