From owner-svn-src-all@freebsd.org Wed Feb 21 15:54:23 2018 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id BE95FF0FA9D; Wed, 21 Feb 2018 15:54:23 +0000 (UTC) (envelope-from emaste@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 715F682CB9; Wed, 21 Feb 2018 15:54:23 +0000 (UTC) (envelope-from emaste@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 685301A98A; Wed, 21 Feb 2018 15:54:23 +0000 (UTC) (envelope-from emaste@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id w1LFsNZC043129; Wed, 21 Feb 2018 15:54:23 GMT (envelope-from emaste@FreeBSD.org) Received: (from emaste@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id w1LFsN3m043128; Wed, 21 Feb 2018 15:54:23 GMT (envelope-from emaste@FreeBSD.org) Message-Id: <201802211554.w1LFsN3m043128@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: emaste set sender to emaste@FreeBSD.org using -f From: Ed Maste Date: Wed, 21 Feb 2018 15:54:23 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r329723 - head/usr.bin/ministat X-SVN-Group: head X-SVN-Commit-Author: emaste X-SVN-Commit-Paths: head/usr.bin/ministat X-SVN-Commit-Revision: 329723 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 21 Feb 2018 15:54:23 -0000 Author: emaste Date: Wed Feb 21 15:54:23 2018 New Revision: 329723 URL: https://svnweb.freebsd.org/changeset/base/329723 Log: ministat: disallow negative variance / nan Stddev With all values identical it was possible for Var() to return a negative value due to limited floating point precision, resulting in "nan" reported as Stddev. Variance cannot actually be negative, so just return 0. We can later investigate alternate algorithms for calculating variance to reduce the effect of catastrophic cancellation here. Reported by: Arshan Khanifar Approved by: phk Sponsored by: The FreeBSD Foundation Modified: head/usr.bin/ministat/ministat.c Modified: head/usr.bin/ministat/ministat.c ============================================================================== --- head/usr.bin/ministat/ministat.c Wed Feb 21 15:51:48 2018 (r329722) +++ head/usr.bin/ministat/ministat.c Wed Feb 21 15:54:23 2018 (r329723) @@ -208,6 +208,12 @@ static double Var(struct dataset *ds) { + /* + * Due to limited precision it is possible that sy^2/n > syy, + * but variance cannot actually be negative. + */ + if (ds->syy <= ds->sy * ds->sy / ds->n) + return (0); return (ds->syy - ds->sy * ds->sy / ds->n) / (ds->n - 1.0); }