From: "H. Peter Anvin" Subject: Re: linux/bitops.h Date: Wed, 4 May 2016 17:30:47 -0700 Message-ID: <572A9437.4020208@zytor.com> References: <1462170413-7164-1-git-send-email-tytso@mit.edu> <1462170413-7164-2-git-send-email-tytso@mit.edu> <20160504174901.GC3901@thunk.org> <20160504190723.GD3901@thunk.org> <572A6CDD.10503@av8n.com> <572A724C.6010704@av8n.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Sasha Levin , Linus Torvalds To: John Denker , tytso@mit.edu, noloader@gmail.com, linux-kernel@vger.kernel.org, Stephan Mueller , Herbert Xu , andi@firstfloor.org, Sandy Harris , cryptography@lakedaemon.net, linux-crypto@vger.kernel.org Return-path: Received: from terminus.zytor.com ([198.137.202.10]:33312 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755447AbcEEAbV (ORCPT ); Wed, 4 May 2016 20:31:21 -0400 In-Reply-To: <572A724C.6010704@av8n.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On 05/04/16 15:06, John Denker wrote: > On 05/04/2016 02:56 PM, H. Peter Anvin wrote: >>> Beware that shifting by an amount >= the number of bits in the >>> word remains Undefined Behavior. > >> This construct has been supported as a rotate since at least gcc2. > > How then should we understand the story told in commit d7e35dfa? > Is the story wrong? > > At the very least, something inconsistent is going on. There > are 8 functions. Why did d7e35dfa change one of them but > not the other 7? Yes. d7e35dfa is baloney IMNSHO. All it does is produce worse code, and the description even says so. As I said, gcc has treated the former code as idiomatic since gcc 2, so that support is beyond ancient. -hpa