From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.help Subject: Re: Bit shift oddity? Date: Mon, 19 Oct 2020 11:14:52 -0400 Message-ID: References: <880f79e9-e2ea-b180-d83f-c3d47f5fb789@gmail.com> <20201019070610.GB9024@tuxteam.de> <3b4def4b-28c5-d549-0645-0056f0709549@gmail.com> <20201019090159.GA11667@tuxteam.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="9294"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:5EGOkTio4vvtXYogmHCY+8seBbg= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Oct 19 17:22:08 2020 Return-path: Envelope-to: geh-help-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 1kUWz9-0002HN-LQ for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 19 Oct 2020 17:22:07 +0200 Original-Received: from localhost ([::1]:45932 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kUWz8-0008BE-Ly for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 19 Oct 2020 11:22:06 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:42402) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kUWsN-0001O2-Hu for help-gnu-emacs@gnu.org; Mon, 19 Oct 2020 11:15:07 -0400 Original-Received: from static.214.254.202.116.clients.your-server.de ([116.202.254.214]:34840 helo=ciao.gmane.io) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kUWsL-0002sf-WC for help-gnu-emacs@gnu.org; Mon, 19 Oct 2020 11:15:07 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1kUWsD-0003mf-I4 for help-gnu-emacs@gnu.org; Mon, 19 Oct 2020 17:14:57 +0200 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/19 11:14:57 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -15 X-Spam_score: -1.6 X-Spam_bar: - X-Spam_report: (-1.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.25, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:124578 Archived-At: > (ash shift (lognot 0)))))) Could there be a simple misunderstanding: the shift amount is the *second* argument. Here you always pass (lognot 0), which is -1, so it's a right shift by 1, IOW a kind of "divide by 2". > shift=-1 res=-1 > shift=-2 res=-1 > shift=-3 res=-2 > shift=-4 res=-2 > shift=-5 res=-3 > shift=-6 res=-3 > shift=-7 res=-4 > shift=-8 res=-4 > shift=-9 res=-5 > shift=-10 res=-5 That does indeed look like divide by 2 to me (rounding toward -∞). Stefan