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 <[email protected]>
> >
> > /*
> > + * 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
http://www.fsdev.dreamhosters.com/wiki/index.php?title=Main_Page
========================================================================
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
