From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29460 invoked by alias); 9 Jan 2003 04:21:14 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 29426 invoked from network); 9 Jan 2003 04:21:12 -0000 Received: from unknown (HELO lacrosse.corp.redhat.com) (66.187.233.200) by 209.249.29.67 with SMTP; 9 Jan 2003 04:21:12 -0000 Received: from free.redhat.lsd.ic.unicamp.br (aoliva.cipe.redhat.com [10.0.1.10]) by lacrosse.corp.redhat.com (8.11.6/8.9.3) with ESMTP id h094KtY11246; Wed, 8 Jan 2003 23:20:55 -0500 Received: from free.redhat.lsd.ic.unicamp.br (localhost.localdomain [127.0.0.1]) by free.redhat.lsd.ic.unicamp.br (8.12.6/8.12.6) with ESMTP id h094KrfL006972; Thu, 9 Jan 2003 02:20:54 -0200 Received: (from aoliva@localhost) by free.redhat.lsd.ic.unicamp.br (8.12.6/8.12.6/Submit) id h094KrSq006967; Thu, 9 Jan 2003 02:20:53 -0200 To: Richard Henderson Cc: "Kaveh R. Ghazi" , gcc-bugs@gcc.gnu.org, gcc-patches@gcc.gnu.org, gcc@gcc.gnu.org, libstdc++@gcc.gnu.org, oldham@codesourcery.com, ro@TechFak.Uni-Bielefeld.DE Subject: Re: Irix6 long doubles implemented wrong? (27_io/ostream_inserter_arith) References: <200212170531.AAA15561@caip.rutgers.edu> <200212241434.JAA22361@caip.rutgers.edu> <20030107221549.GR12992@redhat.com> <20030108220455.GC27635@redhat.com> From: Alexandre Oliva Organization: GCC Team, Red Hat Date: Thu, 09 Jan 2003 09:38:00 -0000 In-Reply-To: Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2003-01/txt/msg00481.txt.bz2 On Jan 9, 2003, Alexandre Oliva wrote: > On Jan 8, 2003, Richard Henderson wrote: >> On Wed, Jan 08, 2003 at 03:17:49PM -0200, Alexandre Oliva wrote: >>> I've no idea of what LIA-1 is, but it does have as many denormal bits >>> as normal bits, it's just that the minimum exponent for a denormal is >>> higher than that of a plain doubles, since denormals start with the >>> higher double still being normal. >> Huh? No it doesn't. The minimum normalized double-double is >> { DBL_MIN_FLT, 0 }. > Nevermind, I was thinking having a denormal in the lower double would > make the whole thing denormal, but in this case the lower double > definitely isn't denormal. On third thought :-), it actually is a denormal, not in the double representation, but in the notion that implies that denormals don't have as much precision as normals. Even though there is an implicit one in the representation of the first double, if you represented the mantissa as a sequence of 106 bits, you'd get this implicit one within the denormal range. The fact that you can represent it as a normal is just an artifact of the long double representation. Well, not really, since the exponent range still enables you to represent it as normal, but it really depends on which aspects of denormals matter. My thought is that loss of mantissa bits is more important than whether there is an implied one next to the MSB of the mantissa, so I'm now trying to model that. This means LDBL_MIN_FLT should be bumped up to represent this fact too, but I suspect this would trigger other sorts of problems, so... There's no Right Thing (TM) to do... Darn, who came up with this long double representation, and why? :-( -- Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/ Red Hat GCC Developer aoliva@{redhat.com, gcc.gnu.org} CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org} Free Software Evangelist Professional serial bug killer