From owner-freebsd-standards@FreeBSD.ORG Sun Nov 30 13:42:23 2003 Return-Path: Delivered-To: freebsd-standards@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B2C8A16A4CE for ; Sun, 30 Nov 2003 13:42:23 -0800 (PST) Received: from VARK.homeunix.com (adsl-68-121-163-164.dsl.pltn13.pacbell.net [68.121.163.164]) by mx1.FreeBSD.org (Postfix) with ESMTP id D2C6843FDF for ; Sun, 30 Nov 2003 13:42:21 -0800 (PST) (envelope-from das@FreeBSD.ORG) Received: from VARK.homeunix.com (localhost [127.0.0.1]) by VARK.homeunix.com (8.12.9/8.12.9) with ESMTP id hAULdpen037486; Sun, 30 Nov 2003 13:39:52 -0800 (PST) (envelope-from das@FreeBSD.ORG) Received: (from das@localhost) by VARK.homeunix.com (8.12.9/8.12.9/Submit) id hAULdprw037485; Sun, 30 Nov 2003 13:39:51 -0800 (PST) (envelope-from das@FreeBSD.ORG) Date: Sun, 30 Nov 2003 13:39:51 -0800 From: David Schultz To: Steve Kargl Message-ID: <20031130213951.GA37082@VARK.homeunix.com> Mail-Followup-To: Steve Kargl , freebsd-standards@FreeBSD.ORG References: <20031129000133.GA30662@troutmask.apl.washington.edu> <20031129080911.GA25448@VARK.homeunix.com> <20031129163105.GA32651@troutmask.apl.washington.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20031129163105.GA32651@troutmask.apl.washington.edu> cc: freebsd-standards@FreeBSD.ORG Subject: Re: Implementing C99's roundf(), round(), and roundl() X-BeenThere: freebsd-standards@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Standards compliance List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 30 Nov 2003 21:42:23 -0000 On Sat, Nov 29, 2003, Steve Kargl wrote: > On Sat, Nov 29, 2003 at 12:09:11AM -0800, David Schultz wrote: > > On Fri, Nov 28, 2003, Steve Kargl wrote: > > > Can the math functions round[fl]() be implemented in > > > terms of other math(3) functions and still conform to the > > > C99 and POSIX standard? For example, > > > > > > #include > > > > > > float roundf(float x) { > > > float t; > > > if (x >= 0.0) { > > > t = ceilf(x); > > > if ((t - x) > 0.5) t -= 1.0; > > > return t; > > > } else { > > > t = ceilf(-x); > > > if ((t + x) > 0.5) t -= 1.0; > > > return -t; > > > } > > > } > > > > This looks correct to me at first glance, modulo possible problems > > with overflow. It's valuable to have simple MI implementations of > > these functions to avoid hampering efforts to port FreeBSD to new > > architectures. Faster MD versions can always be added later. (I > > noticed the other day that Intel has actually released an > > optimized IA64 libm, which we should consider importing.) > > I don't undrestand your overflow comment. ceil[f]() can return Inf > and nan, but in those cases round[f]() should also return Inf and nan. > The two operations, (t-x) and (t+x), should yield a value in the > range [0,1). I'll submit a PR with a man page. The concern was that ceil() could round a number up to infinity when round() is supposed to round the number down. But now that I think about it at a reasonable hour, this concern is clearly bogus. In base two floating point representations, there isn't enough precision to get numbers that large with nonzero fractional parts. > As a side comment, we need to start coding the missing C99 math(3) > functions because GCC is moving to using these in their CVS > development trees. Really? Which ones? I don't think I'll have time to deal with this until January, but then again, we're not doing another gcc import before then.