From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Po Lu Newsgroups: gmane.emacs.devel Subject: Re: Question regarding Lisp_Object representation of symbols Date: Wed, 06 Mar 2024 16:41:16 +0800 Message-ID: <87msrbzr9v.fsf@yahoo.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="35004"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: emacs-devel@gnu.org To: Gerd =?utf-8?Q?M=C3=B6llmann?= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Wed Mar 06 09:42:47 2024 Return-path: Envelope-to: ged-emacs-devel@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 1rhmrO-0008yA-Qo for ged-emacs-devel@m.gmane-mx.org; Wed, 06 Mar 2024 09:42:46 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rhmqh-00035X-BK; Wed, 06 Mar 2024 03:42:03 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rhmqa-00035L-Sz for emacs-devel@gnu.org; Wed, 06 Mar 2024 03:41:56 -0500 Original-Received: from sonic316-22.consmr.mail.ne1.yahoo.com ([66.163.187.148]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1rhmqV-0002tw-Mv for emacs-devel@gnu.org; Wed, 06 Mar 2024 03:41:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1709714509; bh=0pZbfqIDG+rirXRdmeUz56RRmsiFYA36AVsCBMAl5cA=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From:Subject:Reply-To; b=pJtfN4rDldi5rsQ978VDdXh/542G1JBv2PCOP8ecBvEL1Fs+ugUzq9VDcY+uTQIPpdS3w5XmXfaZESLyfjEDJIX/fVPmunlBIUs61nhlTPFOZkBowXctM3f+pIw6IkHtlt49u55y2bmFvlYYY1LKOjVbWxaGtBtqW5hPsPOmizFxbMLt0WntkiR2Sb3R2F0aVqrU/BGp/jfoBoWzS8MbrkTmz/RDctdyGuiexX8jAaBfPTqN/hgj984L+6P1Q44G1gSyDMRlGU73qzqZDrMfc/weVpLbWNFKic/cKiRnI8V/MkGLUxIahwJItlttfn6UlWoD8QUJ42naIJxCkR4PdA== X-SONIC-DKIM-SIGN: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1709714509; bh=pwaQVAASIlTXX1eCFqBZWDsuFpJx+d3fqv7atHBehEQ=; h=X-Sonic-MF:From:To:Subject:Date:From:Subject; b=DvmE87ymRTpJdDdbdM0TV9iLz6DszAnxPHJN+b+RMHvuLOrgjiDGVzTJmXgr91nMJqpcGziXpO3ud6JG8fkymyFMjpQX6gL0u1lEDnPqJUK3NlmQtVSVGKJWbTPg5kc9u/fIg/Lt51CYvKBrvsUent1fDg8TpJaA1pUhkHE0SDfXPPj1wCgYsQ57GwYykTnt/nu5yv6CuCQRo8+kmXxyf0F5OtBpxy/qK3P9qLvHiah8SCtgmZihmPCEFg+Psi8/1VjHY0XrPB2oFmpY+FW18B4al1oSKKQx91zY8zXjbJdlWqTKVlO21yshb7UaHiU7VBzcabdmqB+geUEga/XetA== X-YMail-OSG: npxijkgVM1n0dvXK1oUoD.L52Rrp2o1pZx4G8pal7yAnk6KaxdOYTMZSl5RNcsJ prX.XyYenynVuAxL3iO20emcUPXnAP4HcUD3nU8ThHMttZ87YNfZecfG6zVsYhF.zcLndrOyvTjF bdhAWtgHnAhfZsl1fr7zI5_rLkJVlQooJusgewzJCQ8z1htJLIgi0xXSlKjuKclSa8l8GshtkzpS bFOsa8.LzxL0xZIs9_mbP.PBdUUtKorO8Viart6ca7XO5GcprWN1YEEccsL6pVKehB0DNFptewtP dBH59PBj_3c9lJ2.97mzH1l5NbQAsNXVo1ZCksGB7w23CLwqtIod9u_UQoh3xBGO3pBBZ7EZromt MN7e0bmYty9_BJzxdI1XuZOc8KnrhfaQrKMyb2SyQAW2dYJLGgkIwC9fWulfedXDZuqpPjhtagm3 OHycndYgvSu2NKpzp1yegpGk5E7wl4LqNELGWKB7MqQF76hF2IuEMSguXbEucEAsYHLVR2yHlROx mxsi54ZukNVcXN251Go67K_rGWHXFENyDvxaTJ6lzQPVWamUC5NaXMk3QeLnnUZJLP13Ma9TE3GY sF1aiTsgg8Eauw5_7a_o863opt_1KY6Lf5Qa4weakpSR_KTgZjnKg0A_dWemLTaxezMwnayaw6GV YMUOcLEzsDTM5uF2.GtrRFVjh8EKVH.Kl.F1Mjpselxmlzlcj8llGYQ3KT2oyFSFiYw75wYrXkK9 vew7hAvDiCUgTHPFMH1rSoxh1.T27ocX547Pb8mFlcAsyn1z.a4K5MYcFgw_2FHiCA1lorLdm7Jx qDkETYFh.c2dzdcsz5jnhxas1CZPRPgRT1pcow1xyE X-Sonic-MF: X-Sonic-ID: 0e64c5ec-31b4-48df-b843-9bd5a49a38eb Original-Received: from sonic.gate.mail.ne1.yahoo.com by sonic316.consmr.mail.ne1.yahoo.com with HTTP; Wed, 6 Mar 2024 08:41:49 +0000 Original-Received: by hermes--production-sg3-6dc75bc8fb-n9pfz (Yahoo Inc. Hermes SMTP Server) with ESMTPA ID a4edb64ceae33c86ad28c52ae9778919; Wed, 06 Mar 2024 08:41:41 +0000 (UTC) In-Reply-To: ("Gerd =?utf-8?Q?M=C3=B6llmann?= =?utf-8?Q?=22's?= message of "Wed, 06 Mar 2024 07:48:31 +0100") X-Mailer: WebService/1.1.22129 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.yahoo Received-SPF: pass client-ip=66.163.187.148; envelope-from=luangruo@yahoo.com; helo=sonic316-22.consmr.mail.ne1.yahoo.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:316849 Archived-At: Gerd M=C3=B6llmann writes: > - Does someone remember the reasons why this has been done? To speed up comparisons between objects and Qnil, I think. > - Is there something that relies on this? Maybe something that > relies on 0x0 being a valid Lisp_Object? Yes, in the many places where memset/memclear is invoked to initialize Lisp_Object fields or variables, for instance. It's supposed to be the case that these instances are marked with NIL_IS_ZERO for easy locating if the representation of Qnil is ever to be changed, but that convention is not observed in practice, or is actively circumvented, as by callers of memclear, which defeat the purpose of that marker by calling this one of its bearers to initialize a variety of structures that may or may not comprise only Lisp_Objects, greatly inflating the number of callers that must be examined before such a change in object representation.