On Sun, 19 Oct 2014, at 13:02, Andriy Gapon wrote:
> I think that on platforms where an optimized version of fls() is
> available that
> would work faster than this cool piece of bit magic.
This is a common enough idiom that perhaps a macro should be added:
sys/param.h:
#define roundup(x, y) ((((x)+((y)-1))/(y))*(y)) /* to any y */
#define roundup2(x, y) (((x)+((y)-1))&(~((y)-1))) /* if y is powers of
two */
#define powerof2(x) ((((x)-1)&(x))==0)
sys/amd64/amd64/mp_machdep.c:
/*
* Round up to the next power of two, if necessary, and then
* take log2.
* Returns -1 if argument is zero.
*/
static __inline int
mask_width(u_int x)
{
return (fls(x << (1 - powerof2(x))) - 1);
}
--
BMS (sent via webmail)
_______________________________________________
svn-src-head@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
