Re: [PATCH 1/1] mac80211: improve the contiguous mask checking

On Thu, 2015-12-17 at 22:59 +0800, Zeng Zhaoxiu wrote:

If the result of adding the first set bit to the mask is power of 2,
the mask must be contiguous. "mask & -mask" can get the first set bit
of mask gracefully.

-		if (__ffs64(mask) + hweight64(mask) != fls64(mask))
{
+		inc = (mask & -mask);
+		val = mask + inc;
+		if ((val & (val - 1)) != 0) {
 			/* not a contiguous mask ... not handled now! */

Hm. Ok, I can see how that would work, but it doesn't really seem like
much of an "improvement" to me? Surely I seem to need much more
thinking to understand this. There's no reason to optimise it either,
so why should we change it?

johannes