I recommend that you look at the PRs filed against this class of problem; I
did a quick survey and found:

kern: 495 2978 3459 4084 7668
bin: 2404 3686

I specifically recommend that you look at 3790, 3791 and 3792 which are
Koji Imada's proposed solutions (three different implementations!) to this
problem, which have unfortunately languished since he died in a motorcycle
accident later that year.

All of these PRs can be browsed though http://www.netbsd.org/Misc/query-pr.html
by searching for "512", and hitting the link for each PR.

	better implementations through research,

	Erik <fair@clock.org>