From owner-sc22wg5@open-std.org Thu Sep 23 10:32:29 2004 Return-Path: X-Original-To: sc22wg5-domo Delivered-To: sc22wg5-domo@ghz.klid.dk Received: by ghz.klid.dk (Postfix, from userid 521) id 87B3C37608; Thu, 23 Sep 2004 10:32:29 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from dkuug.dk (ptah.dkuug.dk [195.215.30.66]) by ghz.klid.dk (Postfix) with ESMTP id 2D51A37605 for ; Thu, 23 Sep 2004 10:32:27 +0200 (CET DST) Received: from balin.rl.ac.uk (balin.rl.ac.uk [130.246.135.155]) by dkuug.dk (8.12.10/8.9.2) with ESMTP id i8N8UDjH085335 for ; Thu, 23 Sep 2004 10:30:20 +0200 (CEST) (envelope-from j.k.reid@rl.ac.uk) X-RAL-MFrom: X-RAL-Connect: Received: from jkr.cse.rl.ac.uk (jkr.cse.rl.ac.uk [130.246.9.202]) by balin.rl.ac.uk (8.12.8/8.12.8) with ESMTP id i8N8XHrF008667; Thu, 23 Sep 2004 09:33:19 +0100 Received: from [127.0.0.1] (localhost.localdomain [127.0.0.1]) by jkr.cse.rl.ac.uk (8.12.10/8.12.8) with ESMTP id i8N8Xa87003861; Thu, 23 Sep 2004 09:33:36 +0100 Message-ID: <41528A5F.9070109@rl.ac.uk> Date: Thu, 23 Sep 2004 09:33:35 +0100 From: John Reid Reply-To: j.k.reid@rl.ac.uk Organization: Rutherford Appleton Laboratory User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040803 X-Accept-Language: en-us, en MIME-Version: 1.0 To: WG5 Subject: Forwarded message: RE: Why (standard conforming OR platform implementation) Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.39 X-Spam-Score: 0 () Sender: owner-sc22wg5@open-std.org Precedence: bulk Date: Wed, 22 Sep 2004 14:48:30 -0400 Message-ID: <6E93844AE9173945878F42EB2DBB51B34B0A1D@hdsmsx402.amr.corp.intel.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Why (standard conforming OR platform implementation) Thread-Index: AcSgzs48GIa8BHSkSDmP8Mz7RH0vIQAA6nKg From: "Lionel, Steve" To: "Bernard PICHON" , Cc: "NOULLEZ, Alain" X-OriginalArrivalTime: 22 Sep 2004 18:48:31.0454 (UTC) FILETIME=[C195AFE0:01C4A0D4] X-Scanned-By: MIMEDefang 2.31 (www . roaringpenguin . com / mimedefang) X-Spam-Score: 0 () The problem you're having is due to the use of the Intel X87 floating point registers where calculations involving single precision are actually computed in double precision. For performance, intermediate computations are kept in the registers as long as possible, which can lead to slightly different (though better!) results compared to computations that are rounded to single precision. CVF has a /fltconsistency switch which reduces the effects of this, but it does not help with your program. Intel Fortran offers /Op which does help and gives the result you're looking for, though at a penalty in performance (as /fltconsistency does with CVF). The Alpha system is more "traditional" in that computations are always carried out in the declared precision. The Fortran standard is rather vague when it comes to defining the numerical results of computation. It does not even state that 2+2=3D4! The CVF behavior is standard-conforming. Steve Lionel Software Products Development Intel Corporation Nashua, NH=20 -----Original Message----- From: Bernard PICHON [mailto:Bernard.Pichon@obs-nice.fr]=20 Sent: Wednesday, September 22, 2004 2:11 PM To: sc22wg5@dkuug.dk Cc: NOULLEZ, Alain; Lionel, Steve Subject: Why (standard conforming OR platform implementation) Dear Fortran ! (expands in : Dear WG5 members, dear Lionel) This program seems to me standard conforming. But I don't understand its (different) behavior between Alpha platforms (with True64) for which the result is OK (for me) and Windows/Intel platforms (with CVF V6.6B) with a (very) strange result (in my opinion).