From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: block-sha1: improve code on large-register-set machines Date: Tue, 11 Aug 2009 15:57:10 -0700 (PDT) Message-ID: References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Nicolas Pitre , Git Mailing List , Junio C Hamano To: Brandon Casey X-From: git-owner@vger.kernel.org Wed Aug 12 00:58:30 2009 Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1Mb0IY-0001xI-0C for gcvg-git-2@gmane.org; Wed, 12 Aug 2009 00:58:30 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754622AbZHKW6V (ORCPT ); Tue, 11 Aug 2009 18:58:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754292AbZHKW6V (ORCPT ); Tue, 11 Aug 2009 18:58:21 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:37323 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754124AbZHKW6U (ORCPT ); Tue, 11 Aug 2009 18:58:20 -0400 Received: from imap1.linux-foundation.org (imap1.linux-foundation.org [140.211.169.55]) by smtp1.linux-foundation.org (8.14.2/8.13.5/Debian-3ubuntu1.1) with ESMTP id n7BMvBCm023037 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 11 Aug 2009 15:57:12 -0700 Received: from localhost (localhost [127.0.0.1]) by imap1.linux-foundation.org (8.13.5.20060308/8.13.5/Debian-3ubuntu1.1) with ESMTP id n7BMvADW006494; Tue, 11 Aug 2009 15:57:11 -0700 X-X-Sender: torvalds@localhost.localdomain In-Reply-To: User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) X-Spam-Status: No, hits=-3.463 required=5 tests=AWL,BAYES_00 X-Spam-Checker-Version: SpamAssassin 3.2.4-osdl_revision__1.47__ X-MIMEDefang-Filter: lf$Revision: 1.188 $ X-Scanned-By: MIMEDefang 2.63 on 140.211.169.13 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Tue, 11 Aug 2009, Brandon Casey wrote: > > In that case, why not change the interface of blk_SHA1Block() so that its > second argument is const unsigned char* and get rid of __d and the { } ? Because on big-endian, or on architectures like x86 that have an efficient byte swap, that would be horrible. You absoluetoy MUST NOT do things a byte at a time in those cases. The memory operations and the shifting just kills you. The reason you want to do things a byte at a time on ARM is that ARM cannot do unaligned accesses well (very modern cores are better, but rare), and that ARM has no bswap instruction and has fairly cheap shifts. On no sane architecture is that true. Unaligned loads are fast (and quite frankly, hardware where unaliged loads aren't fast is just crazy sh*t), and doing 'bswap' is way faster than doing many shifts and masks. So everything should be fundamentally word-oriented. Then, broken architectures that can't handle it should split up the words, not the other way around. Linus