From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: integer overflow handling for most-negative-fixnum Date: Sat, 21 Jul 2018 10:48:14 -0700 Organization: UCLA Computer Science Department Message-ID: References: <867elsq78b.fsf@gmail.com> <866018yl76.fsf@gmail.com> <83a7qkzyhz.fsf@gnu.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1532195198 2249 195.159.176.226 (21 Jul 2018 17:46:38 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 21 Jul 2018 17:46:38 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 To: Stefan Monnier , emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Sat Jul 21 19:46:34 2018 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fgvxh-0000Tb-2j for ged-emacs-devel@m.gmane.org; Sat, 21 Jul 2018 19:46:33 +0200 Original-Received: from localhost ([::1]:53453 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fgvzn-0002YY-Uu for ged-emacs-devel@m.gmane.org; Sat, 21 Jul 2018 13:48:43 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:44726) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fgvzd-0002YT-IU for emacs-devel@gnu.org; Sat, 21 Jul 2018 13:48:34 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fgvzY-0002JP-NZ for emacs-devel@gnu.org; Sat, 21 Jul 2018 13:48:33 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:53990) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fgvzO-0002Dz-Es for emacs-devel@gnu.org; Sat, 21 Jul 2018 13:48:28 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id EFED31607DC; Sat, 21 Jul 2018 10:48:16 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id pVVly6evGy_5; Sat, 21 Jul 2018 10:48:15 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 7EE191607F3; Sat, 21 Jul 2018 10:48:15 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id vjBo8gfjK_Tt; Sat, 21 Jul 2018 10:48:15 -0700 (PDT) Original-Received: from [192.168.1.9] (unknown [47.154.30.119]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id E245C1607DC; Sat, 21 Jul 2018 10:48:14 -0700 (PDT) Openpgp: preference=signencrypt Autocrypt: addr=eggert@cs.ucla.edu; prefer-encrypt=mutual; keydata= xsFNBEyAcmQBEADAAyH2xoTu7ppG5D3a8FMZEon74dCvc4+q1XA2J2tBy2pwaTqfhpxxdGA9 Jj50UJ3PD4bSUEgN8tLZ0san47l5XTAFLi2456ciSl5m8sKaHlGdt9XmAAtmXqeZVIYX/UFS 96fDzf4xhEmm/y7LbYEPQdUdxu47xA5KhTYp5bltF3WYDz1Ygd7gx07Auwp7iw7eNvnoDTAl KAl8KYDZzbDNCQGEbpY3efZIvPdeI+FWQN4W+kghy+P6au6PrIIhYraeua7XDdb2LS1en3Ss mE3QjqfRqI/A2ue8JMwsvXe/WK38Ezs6x74iTaqI3AFH6ilAhDqpMnd/msSESNFt76DiO1ZK QMr9amVPknjfPmJISqdhgB1DlEdw34sROf6V8mZw0xfqT6PKE46LcFefzs0kbg4GORf8vjG2 Sf1tk5eU8MBiyN/bZ03bKNjNYMpODDQQwuP84kYLkX2wBxxMAhBxwbDVZudzxDZJ1C2VXujC OJVxq2kljBM9ETYuUGqd75AW2LXrLw6+MuIsHFAYAgRr7+KcwDgBAfwhPBYX34nSSiHlmLC+ KaHLeCLF5ZI2vKm3HEeCTtlOg7xZEONgwzL+fdKo+D6SoC8RRxJKs8a3sVfI4t6CnrQzvJbB n6gxdgCu5i29J1QCYrCYvql2UyFPAK+do99/1jOXT4m2836j1wARAQABzSBQYXVsIEVnZ2Vy dCA8ZWdnZXJ0QGNzLnVjbGEuZWR1PsLBfgQTAQIAKAUCTIByZAIbAwUJEswDAAYLCQgHAwIG FQgCCQoLBBYCAwECH In-Reply-To: Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 131.179.128.68 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 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" Xref: news.gmane.org gmane.emacs.devel:227626 Archived-At: Stefan Monnier wrote: > The only problem I see above is how to *print* > a value like #x-2000000000000000, which is currently done incorrectly. Yes, this is the crux of the matter. > to me both > behaviors are valid and desirable, so we need some way for the > programmer to choose which one to use when How about this idea. First, we extend 'format' to support bitwidth modifi= ers for=20 twos-complement representation. For example, (format "%/24x" -1) would fo= rmat=20 just the low-order 24 bits of the integer, and would return "ffffff" rega= rdless=20 of machine word size or whether bignums are used. Second, we change (format "%x" -1) to return "-1" rather than a=20 machine-dependent string like "3fffffffffffffff" as it does now. That wou= ld make=20 Elisp be more machine-independent, would solve Andy's problem, and would = solve=20 other problems once we have bignums, and in hindsight it's what we should= have=20 done originally. However, it would be an incompatible change, so let's ha= ve the=20 behavior depend on a compatibility variable, much as we already do for=20 read-integer-overflow-as-float.