From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28511 invoked by alias); 26 Mar 2012 16:13:07 -0000 Received: (qmail 28492 invoked by uid 22791); 26 Mar 2012 16:13:04 -0000 X-SWARE-Spam-Status: No, hits=-5.4 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from e2.ny.us.ibm.com (HELO e2.ny.us.ibm.com) (32.97.182.142) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 26 Mar 2012 16:12:52 +0000 Received: from /spool/local by e2.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 26 Mar 2012 12:12:48 -0400 Received: from d01dlp01.pok.ibm.com (9.56.224.56) by e2.ny.us.ibm.com (192.168.1.102) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Mon, 26 Mar 2012 12:10:07 -0400 Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id 8DBF438C8078 for ; Mon, 26 Mar 2012 12:10:03 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q2QGA1DZ198518 for ; Mon, 26 Mar 2012 12:10:01 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q2QG9F6U013200 for ; Mon, 26 Mar 2012 13:09:15 -0300 Received: from spokane1.rchland.ibm.com (spokane1.rchland.ibm.com [9.10.86.94]) by d01av02.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q2QG8r7e010140; Mon, 26 Mar 2012 13:08:53 -0300 Subject: Re: The state of glibc libm From: Steven Munroe Reply-To: munroesj@us.ibm.com To: Vincent Lefevre Cc: "Joseph S. Myers" , libc-alpha@sourceware.org, gcc@gcc.gnu.org, Geert Bosch , Christoph Lauter In-Reply-To: <20120326102605.GD9025@xvii.vinc17.org> References: <20120314143045.GG3804@xvii.vinc17.org> <20120315020743.GH3804@xvii.vinc17.org> <1331826725.7288.6.camel@spokane1.rchland.ibm.com> <20120322161107.GA28285@xvii.vinc17.org> <20120326102605.GD9025@xvii.vinc17.org> Content-Type: text/plain Date: Mon, 26 Mar 2012 16:13:00 -0000 Message-Id: <1332778537.7288.39.camel@spokane1.rchland.ibm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12032616-5112-0000-0000-00000682CBB7 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org X-SW-Source: 2012-03/txt/msg00400.txt.bz2 On Mon, 2012-03-26 at 12:26 +0200, Vincent Lefevre wrote: > On 2012-03-22 16:29:00 +0000, Joseph S. Myers wrote: > > On Thu, 22 Mar 2012, Vincent Lefevre wrote: > > > For the same reason, if the user chose long double instead of > > > double, this may be because he wanted more precision than double. > > > > You mean range? IBM long double provides more precision, but not more > > range. > > Well, precision and/or range. If double precision format is sufficient > for his application, the user can just choose the "double" type. So, > I don't think that it is useful to have long double = double. > > Then concerning double-double vs quad (binary128) for the "long double" > type, I think that quad would be more useful, in particular because > it has been standardized and it is a true FP format. If need be (for > efficiency reasons), double-double could still be implemented using > the "double" type, via a library or ad-hoc code (that does something > more clever, taking the context into account). And the same code (with > just a change of the base type) could be reused to get a double-quad > (i.e. quad + quad) arithmetic, that can be useful to implement the > "long double" versions of the math functions (expl, and so on). > This is much easier said then done. In practice it is a major ABI change and would have to be staged over multiple (7-10) years. > > > So, in the long term, the ABI should probably be changed to have > > > long double = quadruple precision (binary128). > > > > The ABI for Power Architecture changed away from quad precision to using > > IBM long double (the original SysV ABI for PowerPC used quad precision, > > the current ABI uses IBM long double).... > > Perhaps they could change back to quad precision. > That is not the feedback we get from our customers. No one will use software IEEE binary128 and we don't have hardware binary128. So far there is abstract interest but no strong demand for this. So there is no incentive to change.