From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 16789 invoked from network); 19 Sep 2023 11:42:40 -0000 Received: from minnie.tuhs.org (50.116.15.146) by inbox.vuxu.org with ESMTPUTF8; 19 Sep 2023 11:42:40 -0000 Received: from minnie.tuhs.org (localhost [IPv6:::1]) by minnie.tuhs.org (Postfix) with ESMTP id 36C4740429; Tue, 19 Sep 2023 21:42:35 +1000 (AEST) Received: from mercury.lcs.mit.edu (mercury.lcs.mit.edu [18.26.0.122]) by minnie.tuhs.org (Postfix) with ESMTPS id 6EA7640428 for ; Tue, 19 Sep 2023 21:42:30 +1000 (AEST) Received: by mercury.lcs.mit.edu (Postfix, from userid 11178) id 55D3418C084; Tue, 19 Sep 2023 07:42:29 -0400 (EDT) To: tuhs@tuhs.org Message-Id: <20230919114229.55D3418C084@mercury.lcs.mit.edu> Date: Tue, 19 Sep 2023 07:42:29 -0400 (EDT) From: jnc@mercury.lcs.mit.edu (Noel Chiappa) Message-ID-Hash: OAQIUZXIHARXUAO6BXLOV55ASL2EAVYE X-Message-ID-Hash: OAQIUZXIHARXUAO6BXLOV55ASL2EAVYE X-MailFrom: jnc@mercury.lcs.mit.edu X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: jnc@mercury.lcs.mit.edu X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [TUHS] Re: CRC calculation in the 1980s List-Id: The Unix Heritage Society mailing list Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: > From: Paul Ruizendaal > Any suggestions as to why the on-the-fly algorithm did not catch on > more in the 1980's? Maybe it was simply less well known than I think? I can't answer that directly, but I will point you at IEN-56, "CRC Checksum Calculation", by Dave Reed (11-Sep-78): https://www.rfc-editor.org/ien/ien56.pdf Dave wanted the INWG to use a more powerful (in terms of detecting errors) CRC, instead of the simple summation eventually adopted, in TCP and IP. So he produced code to implement a particular CRC, to show people that it would not be particularly expensive (whether in time, or space, I don't alas recall definitively; speed would have been an important consideration, when competing with the summation, though). This would have been close to the leading edge of our knowledge at the time; Dave liked playing around with math, and at about that time he did a very fast DES implementation. Noel