From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Date: Thu, 5 Dec 2019 16:30:44 -0600 From: Bjorn Helgaas Subject: Re: [PATCH v4 7/8] linux/log2.h: Fix 64bit calculations in roundup/down_pow_two() Message-ID: <20191205223044.GA250573@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191203114743.1294-8-nsaenzjulienne@suse.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Nicolas Saenz Julienne Cc: linux-pci@vger.kernel.org, Michael Turquette , "J. Bruce Fields" , linux-nfs@vger.kernel.org, Edward Cree , linux-clk@vger.kernel.org, f.fainelli@gmail.com, Herbert Xu , Emilio =?iso-8859-1?Q?L=F3pez?= , maz@kernel.org, Joerg Roedel , phil@raspberrypi.org, Doug Ledford , Jason Gunthorpe , Chen-Yu Tsai , Chuck Lever , Martin Habets , wahrenst@gmx.net, Tom Lendacky , Jiri Pirko , Solarflare linux maintainers , Maxime Ripard , linux-rpi-kernel@lists.infradead.org, Anna Schumaker , Trond Myklebust , linux-arm-kernel@lists.infradead.org, Mirko Lindner , Mike Marciniszyn , mbrugger@suse.com, Stephen Boyd , netdev@vger.kernel.org, Yishai Hadas , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, jeremy.linton@arm.com, "David S. Miller" , Stephen Hemminger , linux-rdma@vger.kernel.org, iommu@lists.linux-foundation.org, Moni Shoua , Eric Biederman , james.quinlan@broadcom.com, Thomas Graf , andrew.murray@arm.com, Robin Murphy , David Woodhouse , Dennis Dalessandro , Lu Baolu You got the "n" on "down" in the subject, but still missing "of" ;) On Tue, Dec 03, 2019 at 12:47:40PM +0100, Nicolas Saenz Julienne wrote: > Some users need to make sure their rounding function accepts and returns > 64bit long variables regardless of the architecture. Sadly > roundup/rounddown_pow_two() takes and returns unsigned longs. It turns > out ilog2() already handles 32/64bit calculations properly, and being > the building block to the round functions we can rework them as a > wrapper around it. Missing "of" in the function names here. s/a wrapper/wrappers/ IIUC the point of this is that roundup_pow_of_two() returned "unsigned long", which can be either 32 or 64 bits (worth pointing out, I think), and many callers need something that returns "unsigned long long" (always 64 bits). It's a nice simplification to remove the "__" variants. Just as a casual reader of this commit message, I'd like to know why we had both the roundup and the __roundup versions in the first place, and why we no longer need both. > -#define roundup_pow_of_two(n) \ > -( \ > - __builtin_constant_p(n) ? ( \ > - (n == 1) ? 1 : \ > - (1UL << (ilog2((n) - 1) + 1)) \ > - ) : \ > - __roundup_pow_of_two(n) \ > - ) > +#define roundup_pow_of_two(n) \ > +( \ > + (__builtin_constant_p(n) && ((n) == 1)) ? \ > + 1 : (1ULL << (ilog2((n) - 1) + 1)) \ > +) Should the resulting type of this expression always be a ULL, even when n==1, i.e., should it be this? 1ULL : (1ULL << (ilog2((n) - 1) + 1)) \ Or maybe there's no case where that makes a difference? Bjorn _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec