From owner-sc22wg5+sc22wg5-dom8=www.open-std.org@open-std.org Thu Aug 25 02:51:26 2016 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id C74263586F7; Thu, 25 Aug 2016 02:51:26 +0200 (CEST) Delivered-To: sc22wg5@open-std.org Received: from nag-j.co.jp (bvdeuz19.secure.ne.jp [180.222.80.19]) by www.open-std.org (Postfix) with SMTP id D9C743582A1 for ; Thu, 25 Aug 2016 02:51:15 +0200 (CEST) Received: (qmail 82365 invoked from network); 25 Aug 2016 09:51:13 +0900 Received: from unknown (HELO Maru10) (218.42.159.105) by 0 with SMTP; 25 Aug 2016 09:51:13 +0900 Message-ID: <2DE77B7A56D547D097864941DFF54059@Maru10> From: "Cohen Malcolm" To: References: <20160824135715.DE9D535852E@www.open-std.org> In-Reply-To: <20160824135715.DE9D535852E@www.open-std.org> Subject: Re: [ukfortran] (SC22WG5.5784) (j3.2006) edits to clarify SQRTtreatment of negative zero, for comments Date: Thu, 25 Aug 2016 09:51:16 +0900 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="utf-8"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 16.4.3528.331 X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3528.331 Sender: owner-sc22wg5@open-std.org Precedence: bulk >The real part of log of zero is well defined - it is minus infinity. No, the log of real zero is not defined in maths, though it is in a recommended (not mandatory) function in 60559. 60559 does not however define the log of complex zero. According to its usual rules, one might expect (-INF,NaN). >Hence exp( log(x) ) is also well defined - it is zero. Actually that would be (NaN,NaN). >3 out of 3 compilers agree with me And a fourth produces (-Infinity,NaN) (NaN,NaN) Anyway, compilers do not implement maths, nor are they are reliable guide to the finer points of 60559. Also, non-60559 machines exist and are still used, and their compilers cannot agree with you. >Perhaps [we should add more features] Perhaps not at this time. Cheers, -- ........................Malcolm Cohen, Nihon NAG, Tokyo.