Messages in this thread | | | Date | Tue, 30 Jan 2007 07:56:20 -0500 (EST) | From | "Robert P. J. Day" <> | Subject | Re: [PATCH] Add "is_power_of_2" checking to log2.h. |
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On Tue, 30 Jan 2007, Nick Piggin wrote:
> Robert P. J. Day wrote: > > Add the inline function "is_power_of_2()" to log2.h, where the value > > zero is *not* considered to be a power of two. > > > > > Signed-off-by: Robert P. J. Day <rpjday@mindspring.com> > > > > /* > > + * Determine whether some value is a power of two, where zero is > > + * *not* considered a power of two. > > + */ > > Why the qualifier? Zero *is* not a power of 2, is it?
no, but it bears repeating since some developers might think it *is*. if you peruse the current kernel code, you'll find some tests of the simpler form:
((n & (n - 1)) == 0))
which is clearly testing for "power of twoness" but which will return true for a value of zero. that's wrong, and it's why it's emphasized in the comment.
rday
-- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA
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