Messages in this thread | | | Date | Wed, 31 Jan 2007 12:21:46 +1100 | From | Nick Piggin <> | Subject | Re: [PATCH] Add "is_power_of_2" checking to log2.h. |
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Robert P. J. Day wrote: > 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.
I would have thought you'd comment the broken ones, but that's just me.
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