From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Lisp object that refers to a C struct Date: Thu, 18 Oct 2012 19:21:29 +0200 Message-ID: <83r4ov1ysm.fsf@gnu.org> References: <83ehkz4edw.fsf@gnu.org> <83bog33wdr.fsf@gnu.org> <837gqq49j7.fsf@gnu.org> <83r4ox3frd.fsf@gnu.org> <83ipa92i95.fsf@gnu.org> <83bog03jyf.fsf@gnu.org> <507F2C74.4070107@cs.ucla.edu> <83391c2xjq.fsf@gnu.org> <507FADAB.5060108@cs.ucla.edu> <83y5j411fl.fsf@gnu.org> <50803166.6000002@cs.ucla.edu> Reply-To: Eli Zaretskii NNTP-Posting-Host: plane.gmane.org X-Trace: ger.gmane.org 1350580944 29583 80.91.229.3 (18 Oct 2012 17:22:24 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 18 Oct 2012 17:22:24 +0000 (UTC) Cc: emacs-devel@gnu.org To: Paul Eggert Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Oct 18 19:22:31 2012 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1TOtnh-0002Xc-6w for ged-emacs-devel@m.gmane.org; Thu, 18 Oct 2012 19:22:29 +0200 Original-Received: from localhost ([::1]:60804 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOtna-0008MH-25 for ged-emacs-devel@m.gmane.org; Thu, 18 Oct 2012 13:22:22 -0400 Original-Received: from eggs.gnu.org ([208.118.235.92]:46597) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOtnT-0008K6-LC for emacs-devel@gnu.org; Thu, 18 Oct 2012 13:22:20 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TOtnN-0000xA-Qt for emacs-devel@gnu.org; Thu, 18 Oct 2012 13:22:15 -0400 Original-Received: from mtaout23.012.net.il ([80.179.55.175]:33476) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOtnN-0000v6-Im for emacs-devel@gnu.org; Thu, 18 Oct 2012 13:22:09 -0400 Original-Received: from conversion-daemon.a-mtaout23.012.net.il by a-mtaout23.012.net.il (HyperSendmail v2007.08) id <0MC300F00MSM3X00@a-mtaout23.012.net.il> for emacs-devel@gnu.org; Thu, 18 Oct 2012 19:21:12 +0200 (IST) Original-Received: from HOME-C4E4A596F7 ([87.69.4.28]) by a-mtaout23.012.net.il (HyperSendmail v2007.08) with ESMTPA id <0MC300EETMVCXVA0@a-mtaout23.012.net.il>; Thu, 18 Oct 2012 19:21:12 +0200 (IST) In-reply-to: <50803166.6000002@cs.ucla.edu> X-012-Sender: halo1@inter.net.il X-detected-operating-system: by eggs.gnu.org: Solaris 10 (beta) X-Received-From: 80.179.55.175 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:154416 Archived-At: > Date: Thu, 18 Oct 2012 09:42:14 -0700 > From: Paul Eggert > CC: emacs-devel@gnu.org > > On 10/18/2012 04:09 AM, Eli Zaretskii wrote: > >> but in general it's not safe to convert a pointer to > >> > an Emacs fixnum, as this can lose information: the payload > >> > of an Emacs fixnum is typically narrower than a pointer. > > A pointer that is properly aligned has no problem with this. > > It can have problems on hosts where USE_LSB_TAG is 0, > because the conversion to Emacs fixnum can lose high-order > bits in the pointer. We are talking about Windows-specific code, so I don't think this danger is real.