From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: bookkeeping to prepare for a 64-bit EMACS_INT on 32-bit hosts Date: Mon, 02 May 2011 15:12:09 -0300 Message-ID: References: <4DBA71FB.5090900@cs.ucla.edu> <83mxj97889.fsf@gnu.org> <4DBA7F87.5040609@cs.ucla.edu> <4DBB67E2.1040202@cs.ucla.edu> <4DBED72D.9070207@cs.ucla.edu> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1304359943 1329 80.91.229.12 (2 May 2011 18:12:23 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 2 May 2011 18:12:23 +0000 (UTC) Cc: Eli Zaretskii , emacs-devel@gnu.org To: Paul Eggert Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon May 02 20:12:17 2011 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([140.186.70.17]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1QGxbV-0002lm-Lt for ged-emacs-devel@m.gmane.org; Mon, 02 May 2011 20:12:17 +0200 Original-Received: from localhost ([::1]:33634 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QGxbV-0005xE-2K for ged-emacs-devel@m.gmane.org; Mon, 02 May 2011 14:12:17 -0400 Original-Received: from eggs.gnu.org ([140.186.70.92]:35071) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QGxbR-0005x2-IP for emacs-devel@gnu.org; Mon, 02 May 2011 14:12:15 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QGxbQ-0001rj-DH for emacs-devel@gnu.org; Mon, 02 May 2011 14:12:13 -0400 Original-Received: from fencepost.gnu.org ([140.186.70.10]:33636) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QGxbQ-0001re-64 for emacs-devel@gnu.org; Mon, 02 May 2011 14:12:12 -0400 Original-Received: from 121-249-126-200.fibertel.com.ar ([200.126.249.121]:54661 helo=ceviche.home) by fencepost.gnu.org with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1QGxbP-0007Dc-R1; Mon, 02 May 2011 14:12:12 -0400 Original-Received: by ceviche.home (Postfix, from userid 20848) id 11F6366119; Mon, 2 May 2011 15:12:09 -0300 (ART) In-Reply-To: <4DBED72D.9070207@cs.ucla.edu> (Paul Eggert's message of "Mon, 02 May 2011 09:09:17 -0700") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) X-Received-From: 140.186.70.10 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:138972 Archived-At: >>>>> >>> > - /* The EMACS_INT cast avoids a warning. */ >>>>> >>> > + EMACS_INTPTR ii = i; >>>>> >>> > + gpointer gi = (gpointer) ii; >>>> >> Is there a particular reason why you use an intermediate var rather >>>> >> than use the more concise "(gpointer) (EMACS_INTPTR) i"? >>> > To avoid a cast. >> I'm not sure what is the formal definition of "cast" in C, but at least >> from my point of view, your code performs just the same kind of coercion >> as a cast. > The runtime behavior is the same, but avoiding the cast can catch more > errors. Suppose "i" is of type "struct tm *", say, and the programmer > made a mistake. Then GCC will issue a helpful diagnostic for the form > with just one cast, but it won't diagnose the more-concise form with > two casts. Right, implicit coercions are indeed checked more thoroughly since the programmer doesn't say explicitly to shut up. My favorite choice would be to force all casts to have a more easily to find shape (e.g. so `grep' can find them) and to split them into various categories, so the above EMACS_INTPTR cast would be labeled as "checked" or "safe", so the compiler can output warnings. >>> > If you prefer conciseness to avoiding these casts, I can easily change >>> > these to the more-concise form. >> I do prefer the more concise form, and paradoxically part of the reason >> is because it is uses a explicit coercion rather than an implicit one. > OK, will do (unless the above argument convinced you :-). Given that #define checked_cast(t,x) ({ t v = (x); v}) can't be written in ISO C (AFAIK), I either form will be suboptimal, so there's no need to change the code. Stefan