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: Mon, 23 Jul 2018 16:09:54 -0700 Organization: UCLA Computer Science Department Message-ID: <2a7c424e-6a20-2747-8b31-a284be8035a4@cs.ucla.edu> References: <867elsq78b.fsf@gmail.com> <866018yl76.fsf@gmail.com> <83a7qkzyhz.fsf@gnu.org> <56ddf9aa-e7b5-6ab7-bbb8-770e3b0f4c62@cs.ucla.edu> 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 1532387314 8328 195.159.176.226 (23 Jul 2018 23:08:34 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 23 Jul 2018 23:08:34 +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 Tue Jul 24 01:08:30 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 1fhjwK-00023S-OF for ged-emacs-devel@m.gmane.org; Tue, 24 Jul 2018 01:08:28 +0200 Original-Received: from localhost ([::1]:37266 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fhjyR-00082N-HI for ged-emacs-devel@m.gmane.org; Mon, 23 Jul 2018 19:10:39 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:53100) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fhjxo-00082C-HJ for emacs-devel@gnu.org; Mon, 23 Jul 2018 19:10:01 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fhjxk-0001Bj-IK for emacs-devel@gnu.org; Mon, 23 Jul 2018 19:10:00 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:53180) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fhjxk-0001BW-96 for emacs-devel@gnu.org; Mon, 23 Jul 2018 19:09:56 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 092F1160819; Mon, 23 Jul 2018 16:09:55 -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 WKaiBPzsYgud; Mon, 23 Jul 2018 16:09:54 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 5601E160F20; Mon, 23 Jul 2018 16:09:54 -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 4t2IpR20DJmP; Mon, 23 Jul 2018 16:09:54 -0700 (PDT) Original-Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 3C8EE160819; Mon, 23 Jul 2018 16:09:54 -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:227750 Archived-At: On 07/23/2018 12:57 PM, Stefan Monnier wrote: > Another option for the "bitwidth case" is to do it outside of `format`. > I.e. instead of > > (format "%/32x" n) > > you'd use > > (format "%x" (truncate-to-bitwidth n 32)) > > where `truncate-to-bitwidth` would turn a negative number into its > positive equivalent (mod 2^bitwidth). That shouldn't be too hard to > implement in Elisp once we have bignums. Yes, with bignums it can be implemented this way, if I understand you=20 aright: (defun truncate-to-bitwidth (num bits) =C2=A0 (logand num (- (lsh 1 bits) 1)))