From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756500AbYGYUsR (ORCPT ); Fri, 25 Jul 2008 16:48:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750827AbYGYUsF (ORCPT ); Fri, 25 Jul 2008 16:48:05 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:35449 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751343AbYGYUsE (ORCPT ); Fri, 25 Jul 2008 16:48:04 -0400 Date: Fri, 25 Jul 2008 13:47:59 -0700 From: Andrew Morton To: "H. Peter Anvin" Cc: joerg.roedel@amd.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] introduce lower_32_bits() macro Message-Id: <20080725134759.ae19b883.akpm@linux-foundation.org> In-Reply-To: <4889FA03.6010708@zytor.com> References: <1216998747-16896-1-git-send-email-joerg.roedel@amd.com> <4889FA03.6010708@zytor.com> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 25 Jul 2008 12:06:27 -0400 "H. Peter Anvin" wrote: > Joerg Roedel wrote: > > The file kernel.h contains the upper_32_bits macro. This patch adds the other > > part, the lower_32_bits macro. Its first use will be in the driver for AMD > > IOMMU. > > > > Signed-off-by: Joerg Roedel > > --- > > include/linux/kernel.h | 6 ++++++ > > 1 files changed, 6 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > > index f9cd7a5..6fd2977 100644 > > --- a/include/linux/kernel.h > > +++ b/include/linux/kernel.h > > @@ -73,6 +73,12 @@ extern const char linux_proc_banner[]; > > */ > > #define upper_32_bits(n) ((u32)(((n) >> 16) >> 16)) > > > > +/** > > + * lower_32_bits - return bits 0-31 of a number > > + * @n: the number we're accessing > > + */ > > +#define lower_32_bits(n) ((n) & 0xffffffffULL) > > + > > NAK. These are assymmetric with regards to type, which is the *last* > thing we want. Yes, it will convert a 32-bit expression into a 64-bit one. > The symmetric definition would be ((u32)(n)), but that's already > idiomatic use, so why not use it as-is? There's some readability benefit. Sometimes it is hard to understand why some random open-coded cast was used. But I seem to recall that there was another reason why we decided we needed this. I forget, and so apparently did the changelog author ;)