From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.ciao.gmane.io!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#41544: 26.3; Possible incorrect results from color-distance Date: Tue, 02 Jun 2020 19:14:28 +0300 Message-ID: <83y2p5cumz.fsf@gnu.org> References: <5C4A633D-8222-4439-BE37-9B8674F1DA6D@acm.org> <87r1v2aat3.fsf@tromey.com> <9902865C-01B4-4E50-A433-DBC8B8311234@acm.org> <83tuzueogo.fsf@gnu.org> <6272275C-560C-4437-90F1-2A8294D27019@acm.org> <83o8q2elja.fsf@gnu.org> <83mu5mel4o.fsf@gnu.org> <77F1DDD3-A69F-40ED-902D-74986D5E6596@acm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="ciao.gmane.io:159.69.161.202"; logging-data="51724"; mail-complaints-to="usenet@ciao.gmane.io" Cc: tom@tromey.com, simon@polaris64.net, 41544@debbugs.gnu.org To: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Tue Jun 02 18:16:49 2020 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jg9ar-000DK9-Qe for geb-bug-gnu-emacs@m.gmane-mx.org; Tue, 02 Jun 2020 18:16:49 +0200 Original-Received: from localhost ([::1]:43566 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jg9aq-0002lu-NL for geb-bug-gnu-emacs@m.gmane-mx.org; Tue, 02 Jun 2020 12:16:48 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:33258) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jg9a7-0001S5-0C for bug-gnu-emacs@gnu.org; Tue, 02 Jun 2020 12:16:03 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:57415) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jg9a6-0006Tg-KN for bug-gnu-emacs@gnu.org; Tue, 02 Jun 2020 12:16:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1jg9a6-0001E4-Ft for bug-gnu-emacs@gnu.org; Tue, 02 Jun 2020 12:16:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Tue, 02 Jun 2020 16:16:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 41544 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: patch Original-Received: via spool by 41544-submit@debbugs.gnu.org id=B41544.15911145044635 (code B ref 41544); Tue, 02 Jun 2020 16:16:02 +0000 Original-Received: (at 41544) by debbugs.gnu.org; 2 Jun 2020 16:15:04 +0000 Original-Received: from localhost ([127.0.0.1]:40728 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jg9Z9-0001Ch-Pz for submit@debbugs.gnu.org; Tue, 02 Jun 2020 12:15:04 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:53902) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1jg9Z8-0001Bu-4t for 41544@debbugs.gnu.org; Tue, 02 Jun 2020 12:15:02 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:47539) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jg9Z2-0005Z8-A0; Tue, 02 Jun 2020 12:14:56 -0400 Original-Received: from [176.228.60.248] (port=4300 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1jg9Ys-0006Sn-UG; Tue, 02 Jun 2020 12:14:55 -0400 In-Reply-To: <77F1DDD3-A69F-40ED-902D-74986D5E6596@acm.org> (message from Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= on Tue, 2 Jun 2020 17:27:46 +0200) X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:181410 Archived-At: > From: Mattias Engdegård > Date: Tue, 2 Jun 2020 17:27:46 +0200 > Cc: tom@tromey.com, simon@polaris64.net, 41544@debbugs.gnu.org > > Let's start with the color-distance changes, out of respect for the bug reporter if nothing else. > > It is not possible to change a function without changing it. Either we fix it or we don't. The reported bug was about broken symmetry, which is rather embarrassing; as written previously, the first analysis uncovered deeper issues worth fixing, such as loss of precision and (especially) the nonlinearity that causes triangle inequality violation. > > The proposed fixes to color-distance, I hope you agree, are straightforward, reasonable and address all these points. Callers have been updated with carefully recomputed comparison constants; I detailed how they were obtained in a previous reply, and test have all been satisfactory. I'd prefer to fix only the symmetry bug (which AFAIU happens because we use bit shifts on signed integers), without introducing any other effects on the function's behavior and return values. AFAIU, such a fix should not require any changes outside of the function itself. OK?