linux-kernel - Re: [PATCH] Add "is_power_of

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Pine.LNX.4.64.0701301058300.24690@CPE00045a9c397f-CM001225dbafb6>
Date:	Tue, 30 Jan 2007 11:00:07 -0500 (EST)
From:	"Robert P. J. Day" <rpjday@...dspring.com>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Paul Mackerras <paulus@...ba.org>, dhowells@...hat.com,
	galak@...nel.crashing.org
Subject: Re: [PATCH] Add "is_power_of_2" checking to log2.h.

On Tue, 30 Jan 2007, Jan Engelhardt wrote:

>
> On Jan 30 2007 09:45, Robert P. J. Day wrote:

> >seriously, though, there is the potential of breaking something with
> >this change since you can see how there is some inconsistency in how
> >it's done *now* just for powerpc which, in some places, defines its
> >own versions of this:
> >
> >./arch/ppc/mm/pgtable.c:
> >	#define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
> >./arch/ppc/syslib/ppc85xx_rio.c:
> >	#define is_power_of_2(x) (((x) & ((x) - 1)) == 0)
> >./arch/powerpc/mm/pgtable_32.c:
> >	#define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
> >
> >note how the first and third macros *won't* consider zero a power of
> >two, while the second one *will*.  hence the need for a single
> >standard for all of this, just to play it safe.
>
> Hmpf. Perhaps a second macro "is_intdivisible_by_power_of_2" or so could
> catch the "am I zero or 2^n" question.

no.  if that's really what the programmer wants, they can code it that
way explicitly.  let's not make this overly obscure.

rday
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/