once upon a time, the kernel source code was replete with
conditional constructs of the form:
if ((n & (n-1)) == 0)
as a way of testing whether something was a power of two. mercifully,
include/linux/log2.h was created which introduced, among other things:
static inline __attribute__((const))
bool is_power_of_2(unsigned long n)
{
return (n != 0 && ((n & (n - 1)) == 0));
}
so we could simply ask whether "is_power_of_2(n)", which is convenient
when we're testing things like, oh, blocksize.
similarly, there are bunches of places which need to test whether an
integer value has only a single set bit (for instance, to make sure
only one flag bit out of a number of mutually exclusive bits are set).
mathematically, that would be the same test, of course, but
semantically, it would be ugly and inappropriate. is there,
somewhere, a corresponding macro/function that asks:
single_bit_set(n)
if not, that would be handy, could be plopped into
include/linux/bitops.h and could be defined exactly the same way, and
would allow piles of code to be simplified.
thoughts?
rday
--
========================================================================
Robert P. J. Day Waterloo, Ontario, CANADA
Linux Consulting, Training and Annoying Kernel Pedantry.
Web page: http://crashcourse.ca
Linked In: http://www.linkedin.com/in/rpjday
Twitter: http://twitter.com/rpjday
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