From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: ptrdiff_t misuse Date: Fri, 06 Jul 2012 07:56:48 -0700 Organization: UCLA Computer Science Department Message-ID: <4FF6FCB0.8080400@cs.ucla.edu> References: <83lij66yq9.fsf@gnu.org> <4FEDB953.1010800@yandex.ru> <4FEEA720.2040405@cs.ucla.edu> <4FEEFBAB.6000404@cs.ucla.edu> <4FF3E1D6.1050103@cs.ucla.edu> <83bojv4h13.fsf@gnu.org> <4FF48920.501@cs.ucla.edu> <83vci22mr0.fsf@gnu.org> <83obnu2e8s.fsf@gnu.org> <4FF62C92.8090406@cs.ucla.edu> <83liix2xvp.fsf@gnu.org> <4FF69476.2070701@cs.ucla.edu> <83ipe12s6r.fsf@gnu.org> <8739556vjm.fsf@uwakimon.sk.tsukuba.ac.jp> <83bojt2lwm.fsf@gnu.org> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Trace: dough.gmane.org 1341586636 13646 80.91.229.3 (6 Jul 2012 14:57:16 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Fri, 6 Jul 2012 14:57:16 +0000 (UTC) Cc: "Stephen J. Turnbull" , dmantipov@yandex.ru, monnier@iro.umontreal.ca, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Jul 06 16:57:12 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 1Sn9y0-00043B-94 for ged-emacs-devel@m.gmane.org; Fri, 06 Jul 2012 16:57:08 +0200 Original-Received: from localhost ([::1]:55170 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sn9xy-0001dE-Vu for ged-emacs-devel@m.gmane.org; Fri, 06 Jul 2012 10:57:06 -0400 Original-Received: from eggs.gnu.org ([208.118.235.92]:33533) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sn9xv-0001cU-MI for emacs-devel@gnu.org; Fri, 06 Jul 2012 10:57:05 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Sn9xp-00022p-Hg for emacs-devel@gnu.org; Fri, 06 Jul 2012 10:57:03 -0400 Original-Received: from smtp.cs.ucla.edu ([131.179.128.62]:55408) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sn9xj-00021j-Od; Fri, 06 Jul 2012 10:56:51 -0400 Original-Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp.cs.ucla.edu (Postfix) with ESMTP id 9300AA6001D; Fri, 6 Jul 2012 07:56:49 -0700 (PDT) X-Virus-Scanned: amavisd-new at smtp.cs.ucla.edu Original-Received: from smtp.cs.ucla.edu ([127.0.0.1]) by localhost (smtp.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3kzVNcIHyGuF; Fri, 6 Jul 2012 07:56:49 -0700 (PDT) Original-Received: from [192.168.1.4] (pool-108-23-119-2.lsanca.fios.verizon.net [108.23.119.2]) by smtp.cs.ucla.edu (Postfix) with ESMTPSA id 0B556A60001; Fri, 6 Jul 2012 07:56:49 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 In-Reply-To: <83bojt2lwm.fsf@gnu.org> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) X-Received-From: 131.179.128.62 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:151454 Archived-At: On 07/06/2012 04:01 AM, Eli Zaretskii wrote: > It is easy enough to explain that EMACS_POS is used for Lisp integers > that express buffer and string positions, and EMACS_INT for any other > Lisp integer values. But not every use of ptrdiff_t is for buffer and string positions. Bitmap table sizes, for example. So we would need three types: EMACS_INT for Lisp integer values EMACS_POS for buffer and string positions ptrdiff_t for other large memory-related numbers and at that point, we'll need to teach Emacs hackers about ptrdiff_t anyway. An argument for EMACS_POS is that it clearly identifies an integer as being used for a buffer or a string position, as having some other ptrdiff_t-like use. But in that case shouldn't we also distinguish between buffer positions and string positions? And distinguish between character and byte counts, in both cases? Something like this? EMACS_INT for Lisp integer values EMACS_BUFCPOS for buffer char positions EMACS_BUFBPOS for buffer byte positions EMACS_STRCPOS for string char positions EMACS_STRBPOS for string byte positions ptrdiff_t for other large memory-related numbers This question answers itself, I think -- the extra complexity isn't worth it, and we should stick with EMACS_INT and ptrdiff_t. I think most competent C programmers know ptrdiff_t well enough. They think of it being like size_t, but signed. Other GNU software tends to prefer size_t, but the Emacs style is to prefer signed integers and ptrdiff_t is the obvious alternative. I agree that most C programs use 'int' for indexes, but that's because they're small indexes. Emacs does this too, when indexes are known to be sufficiently small.