From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Gregory Heytings via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: Bit shift oddity? Date: Mon, 19 Oct 2020 09:23:04 +0000 Message-ID: References: <880f79e9-e2ea-b180-d83f-c3d47f5fb789@gmail.com> Reply-To: Gregory Heytings Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="12570"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Alpine 2.22 (NEB 394 2020-01-19) Cc: help-gnu-emacs To: Douglas Lewan Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Oct 19 11:24:45 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 1kURPJ-0003Aq-3G for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 19 Oct 2020 11:24:45 +0200 Original-Received: from localhost ([::1]:46266 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kURPI-0003ci-68 for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 19 Oct 2020 05:24:44 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:46342) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kURNs-0002gq-3u for help-gnu-emacs@gnu.org; Mon, 19 Oct 2020 05:23:16 -0400 Original-Received: from mx.sdf.org ([205.166.94.24]:49327) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kURNp-0007lc-24 for help-gnu-emacs@gnu.org; Mon, 19 Oct 2020 05:23:14 -0400 Original-Received: from sdf.org (IDENT:ghe@faeroes.freeshell.org [205.166.94.9]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 09J9N7ve025231 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Mon, 19 Oct 2020 09:23:07 GMT Original-Received: (from ghe@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 09J9N7hw028926; Mon, 19 Oct 2020 09:23:07 GMT In-Reply-To: <880f79e9-e2ea-b180-d83f-c3d47f5fb789@gmail.com> Received-SPF: pass client-ip=205.166.94.24; envelope-from=ghe@sdf.org; helo=mx.sdf.org X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/19 04:46:59 X-ACL-Warn: Detected OS = ??? X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham 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:124575 Archived-At: > > I see the following: > > ELISP> (= (lsh -1 (lognot 0)) (lsh -2 (lognot 0))) > > t > > ELISP> (= (lsh -1 (lognot 0)) (lsh -3 (lognot 0))) > > nil > > The first seems odd to me. Is it really what's expected? > Yes, it's what is expected. The docstring of lsh says: "(lsh VALUE COUNT) ... If COUNT is negative, shifting is actually to the right. In this case, if VALUE is a negative fixnum treat it as unsigned ..." -1 (decimal) = 111...111 (binary) -2 (decimal) = 111...110 (binary) If you shift these two numbers to the right, you get the exact same result: 011...111, that is, `most-positive-fixnum'.