From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: AI12-0218: What is the portable representation clause for processing IETF packets on little-endian machines? Date: Thu, 10 May 2018 21:34:35 +0200 Organization: Aioe.org NNTP Server Message-ID: References: NNTP-Posting-Host: kQkuQcRDy1QFvWpyB1foYw.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 X-Notice: Filtered by postfilter v. 0.8.3 Content-Language: en-US Xref: reader02.eternal-september.org comp.lang.ada:52206 Date: 2018-05-10T21:34:35+02:00 List-Id: On 2018-05-10 19:45, Dan'l Miller wrote: > It seems that 2 major use-cases of AI12-0218 are getting short shrift. > > http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ai12s/ai12-0218-1.txt?rev=1.3&raw=N [...] > The Challenge: > Without the proposed solution in AI12-0218, I challenge anyone to write an Ada representation clause that is •portable• to both little-endian and big-endian processors for either of the following IETF packet formats that must always be in big-endian network byte order: > https://en.wikipedia.org/wiki/IPv4#Packet_structure > https://en.wikipedia.org/wiki/IPv6_packet Representation clauses are useless for network protocols and serialization, for multiple reasons. I never used them in any of the protocol implementations I wrote. The only place representation clauses could have is mapping special machine registers, which naturally excludes any questions of portability. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de