From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: Byte swapping and bindat Date: Fri, 10 Jun 2022 13:03:46 -0400 Message-ID: References: <87pmjglllc.fsf.ref@yahoo.com> <87pmjglllc.fsf@yahoo.com> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="1671"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:AcwgKuL/N366e0G4rVrpKApLdoc= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Fri Jun 10 19:04:26 2022 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1nzi3d-00009P-RZ for geh-help-gnu-emacs@m.gmane-mx.org; Fri, 10 Jun 2022 19:04:25 +0200 Original-Received: from localhost ([::1]:59456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nzi3c-0006Xn-M0 for geh-help-gnu-emacs@m.gmane-mx.org; Fri, 10 Jun 2022 13:04:24 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:47672) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzi3A-0006VO-DN for help-gnu-emacs@gnu.org; Fri, 10 Jun 2022 13:03:56 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:58782) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzi37-0007LS-JI for help-gnu-emacs@gnu.org; Fri, 10 Jun 2022 13:03:55 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1nzi35-0009lD-9u for help-gnu-emacs@gnu.org; Fri, 10 Jun 2022 19:03:51 +0200 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:137615 Archived-At: Stefan Monnier via Users list for the GNU Emacs text editor [2022-06-10 09:32:31] wrote: >> Is there a way to specify a bindat type with fields whose endianess >> depends on an external parameter (or another field of the type?) > > I'm so glad you asked: > > (let* ((threshold 32) > (type (bindat-type (kind uint 8) > (length sint 32 (> kind threshold))))) > (list (bindat-unpack type "\x10\x00\x00\x01\x01") > (bindat-unpack type "\x80\x00\x00\x01\x01"))) > => > (((kind . 16) (length . 257)) > ((kind . 128) (length . 16842752))) > > That's one of the benefits of the new Bindat :-) Oh, and if you want to do that for `uint` (which currently doesn't take a "reverse" argument (patch welcome)), you can do: (let* ((threshold 32) (type (bindat-type (kind uint 8) (length if (> kind threshold) (uintr 32) (uint 32))))) (list (bindat-unpack type "\x10\x00\x00\x01\x01") (bindat-unpack type "\x80\x00\x00\x01\x01"))) => (((kind . 16) (length . 257)) ((kind . 128) (length . 16842752))) -- Stefan