From owner-freebsd-numerics@FreeBSD.ORG Sun Aug 12 23:07:34 2012 Return-Path: Delivered-To: freebsd-numerics@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 154CC106566C for ; Sun, 12 Aug 2012 23:07:34 +0000 (UTC) (envelope-from peter@rulingia.com) Received: from vps.rulingia.com (host-122-100-2-194.octopus.com.au [122.100.2.194]) by mx1.freebsd.org (Postfix) with ESMTP id 9CAF48FC16 for ; Sun, 12 Aug 2012 23:07:33 +0000 (UTC) Received: from server.rulingia.com (c220-239-249-137.belrs5.nsw.optusnet.com.au [220.239.249.137]) by vps.rulingia.com (8.14.5/8.14.5) with ESMTP id q7CN7XYe075726 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 13 Aug 2012 09:07:33 +1000 (EST) (envelope-from peter@rulingia.com) X-Bogosity: Ham, spamicity=0.000000 Received: from server.rulingia.com (localhost.rulingia.com [127.0.0.1]) by server.rulingia.com (8.14.5/8.14.5) with ESMTP id q7CN7Rkk021400 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Mon, 13 Aug 2012 09:07:27 +1000 (EST) (envelope-from peter@server.rulingia.com) Received: (from peter@localhost) by server.rulingia.com (8.14.5/8.14.5/Submit) id q7CN7Rld021399 for freebsd-numerics@freebsd.org; Mon, 13 Aug 2012 09:07:27 +1000 (EST) (envelope-from peter) Resent-From: Peter Jeremy Resent-Date: Mon, 13 Aug 2012 09:07:27 +1000 Resent-Message-ID: <20120812230727.GA20453@server.rulingia.com> Resent-To: freebsd-numerics@freebsd.org Received: from vps.rulingia.com (host-122-100-2-194.octopus.com.au [122.100.2.194]) by server.rulingia.com (8.14.5/8.14.5) with ESMTP id q6IKuUBN005285 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Thu, 19 Jul 2012 06:56:31 +1000 (EST) (envelope-from sgk@troutmask.apl.washington.edu) Received: from troutmask.apl.washington.edu (troutmask.apl.washington.edu [128.95.76.21]) by vps.rulingia.com (8.14.5/8.14.5) with ESMTP id q6IKuSf4078098 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Thu, 19 Jul 2012 06:56:29 +1000 (EST) (envelope-from sgk@troutmask.apl.washington.edu) Received: from troutmask.apl.washington.edu (localhost.apl.washington.edu [127.0.0.1]) by troutmask.apl.washington.edu (8.14.5/8.14.5) with ESMTP id q6IKuQ5O000438; Wed, 18 Jul 2012 13:56:26 -0700 (PDT) (envelope-from sgk@troutmask.apl.washington.edu) Received: (from sgk@localhost) by troutmask.apl.washington.edu (8.14.5/8.14.5/Submit) id q6IKuPFC000437; Wed, 18 Jul 2012 13:56:25 -0700 (PDT) (envelope-from sgk) From: Steve Kargl Mail-Followup-To: freebsd-numerics@freebsd.org To: Stephen Montgomery-Smith Message-ID: <20120718205625.GA409@troutmask.apl.washington.edu> References: <201207130818.38535.jhb@freebsd.org> <9EB2DA4F-19D7-4BA5-8811-D9451CB1D907@theravensnest.org> <20120713155805.GC81965@zim.MIT.EDU> <20120714120432.GA70706@server.rulingia.com> <20120717084457.U3890@besplex.bde.org> <5004A5C7.1040405@missouri.edu> <5004DEA9.1050001@missouri.edu> <20120717200931.U6624@besplex.bde.org> <5006D13D.2080702@missouri.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5006D13D.2080702@missouri.edu> User-Agent: Mutt/1.4.2.3i Cc: Diane Bruce , John Baldwin , David Chisnall , Bruce Evans , Bruce Evans , David Schultz , Peter Jeremy , Warner Losh Subject: Re: Use of C99 extra long double math functions after r236148 X-BeenThere: freebsd-numerics@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Discussions of high quality implementation of libm functions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Date: Sun, 12 Aug 2012 23:07:34 -0000 X-Original-Date: Wed, 18 Jul 2012 13:56:25 -0700 X-List-Received-Date: Sun, 12 Aug 2012 23:07:34 -0000 On Wed, Jul 18, 2012 at 10:07:41AM -0500, Stephen Montgomery-Smith wrote: > > >The most obvious immediate difficulty in translating the above into C is > >that y*y and z*z may overflow when the result shouldn't. > > This will be a lot easier than I originally expected. When we are in > conditions when overflow might occur, we can simply make the approximations > sqrt(y*y-1) = y > csqrt(z*z+1) = signum(x)*z > because in floating point arithmetic, these will not be approximations, > but true exactly. And I am thinking that the test I will use for when > to use these approximations will be (y==y+1) and (z==z+1) respectively. > (I would use (z*z==z*z+1) but that test has the overflow problem.) I could be mistaken, but I believe that you need to raise the inexact flag with these approximations because in fact you are doing floating point math. -- Steve