From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Message-ID: Subject: Re: [PATCH v4 7/8] linux/log2.h: Fix 64bit calculations in roundup/down_pow_two() From: Nicolas Saenz Julienne Date: Thu, 12 Dec 2019 14:16:27 +0100 In-Reply-To: <20191205223044.GA250573@google.com> References: <20191205223044.GA250573@google.com> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============1584875826772588478==" Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Bjorn Helgaas 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 --===============1584875826772588478== Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-vpJ9shRBsDfxzY4jD4N5" --=-vpJ9shRBsDfxzY4jD4N5 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2019-12-05 at 16:30 -0600, Bjorn Helgaas wrote: > You got the "n" on "down" in the subject, but still missing "of" ;) Yes, sorry about that, I tend to re-read what I meant to say instead of wha= t it's actually written. > 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 return= s > > 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. >=20 > Missing "of" in the function names here. > s/a wrapper/wrappers/ Noted > 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). I'll update the commit message to be a more explicit. > 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. So, the commit that introduced it (312a0c170945b) meant to use the '__' var= iant as a helper, but, due to the fact this is a header file, some found it and = made use of it. I went over some if the commits introducing '__' usages and none= of them seem to acknowledge its use as opposed to the macro version. I think i= t's fair to say it's a case of cargo-culting. > > -#define roundup_pow_of_two(n) \ > > -( \ > > - __builtin_constant_p(n) ? ( \ > > - (n =3D=3D 1) ? 1 : \ > > - (1UL << (ilog2((n) - 1) + 1)) \ > > - ) : \ > > - __roundup_pow_of_two(n) \ > > - ) > > +#define roundup_pow_of_two(n) \ > > +( \ > > + (__builtin_constant_p(n) && ((n) =3D=3D 1)) ? \ > > + 1 : (1ULL << (ilog2((n) - 1) + 1)) \ > > +) >=20 > Should the resulting type of this expression always be a ULL, even > when n=3D=3D1, i.e., should it be this? >=20 > 1ULL : (1ULL << (ilog2((n) - 1) + 1)) \ >=20 > Or maybe there's no case where that makes a difference? It should be 1ULL on either case. Regards, Nicolas --=-vpJ9shRBsDfxzY4jD4N5 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl3yPasACgkQlfZmHno8 x/4qrgf9GTaIX4ZRG0TCYwOuyJCzR/7cg3GMSsuHo8bknRFfBKmZUwtS0JmNNrn7 f1Av7IZ0OAbAWPJQkzOXw4OxNhVxq0ItdXAktetVKaF6U5Dz/5tWkkwHLFdhSepV FcS4qxWo8nOugcgYRzN6kDaihMFUqbAIioU7n1HGLRGN2s9vaJM1rNmOrGMPovU3 BbGTs4/7BMM3FmqoGwWUKX5FPFNamYrxAaaOknMUVa16iI7MN7hYH5scWUUK56ER 57y4jC6vGu17Cku4HBlynsoZpm6z6SvHDoXIMZCbUKbJogsiQo+b1+cZTWLVGi2P qQGX/jHjIhYWNVa2Le9F3qgxxmf0uA== =hg1F -----END PGP SIGNATURE----- --=-vpJ9shRBsDfxzY4jD4N5-- --===============1584875826772588478== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec --===============1584875826772588478==--