Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754382Ab0AINpW (ORCPT ); Sat, 9 Jan 2010 08:45:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753160Ab0AINpU (ORCPT ); Sat, 9 Jan 2010 08:45:20 -0500 Received: from mga02.intel.com ([134.134.136.20]:65455 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751254Ab0AINpT (ORCPT ); Sat, 9 Jan 2010 08:45:19 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.49,247,1262592000"; d="scan'208";a="585754584" Date: Sat, 9 Jan 2010 21:44:56 +0800 From: Wu Fengguang To: Jamie Lokier Cc: Roland Dreier , Andrew Morton , David Miller , Stephen Rothwell , Al Viro , Christoph Hellwig , Eric Paris , LKML , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH] fs: O_* bit numbers uniqueness check Message-ID: <20100109134456.GC20015@localhost> References: <20100106065526.GB11368@localhost> <20100106162004.GA11773@shareable.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100106162004.GA11773@shareable.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2309 Lines: 68 On Thu, Jan 07, 2010 at 12:20:04AM +0800, Jamie Lokier wrote: > Roland Dreier wrote: > > > > > + /* please add new bits here to ensure allocation uniqueness */ > > > + BUG_ON(20 != hweight32( > > > + O_RDONLY | O_WRONLY | O_RDWR | > > > > I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is > > caught at compile time (a change like adding an O_ flag is often compile > > tested only for obscure archs). One could create a compile-time > > macro-ized version of hweight32() and use that, I guess, although I'm > > not sure it's worth the ugliness. > > Not ugly at all: > > #define hweight32(x) __builtin_popcount(x) > > Checked GCC 3.4.3 / 4.1 / 4.4: It expands as a compile-time constant > if the argument is a compile-time constant, so can be used in > BUILD_BUG_ON() and even for array sizes etc. > > If GCC's __builtin_popcount() isn't good enough for non-constant > values, the macro would be more involved: > > #define hweight32(x) (__builtin_constant_p(x) ? __builtin_popcount(x) \ > : hweight32_nonconstant(x)) Jamie, Thanks for the hint! Would you sign this patch? --- bitops: compile time optimization for hweight_long(CONSTANT) This allows use of hweight_long() in BUILD_BUG_ON(). Suggested by Jamie. CC: Jamie Lokier CC: Roland Dreier Signed-off-by: Wu Fengguang --- include/linux/bitops.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) --- linux.orig/include/linux/bitops.h 2010-01-09 12:13:00.000000000 +0800 +++ linux/include/linux/bitops.h 2010-01-09 12:21:50.000000000 +0800 @@ -40,10 +40,14 @@ static __inline__ int get_count_order(un return order; } -static inline unsigned long hweight_long(unsigned long w) -{ - return sizeof(w) == 4 ? hweight32(w) : hweight64(w); -} +#define hweight_long(x) \ +( \ + __builtin_constant_p(x) ? \ + __builtin_popcountl(x) : \ + (sizeof(x) <= 4 ? \ + hweight32(x) : \ + hweight64(x)) \ +) /** * rol32 - rotate a 32-bit value left -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/