Position sorting

[Adam Wiggins]

A while back (I can't remember how long, maybe a year or so)
someone posted the basics for an algorithm which involved
interpolating the bits of an object's coordinates in game space
in order to generate a sorting key.  Recently something came up
that made me think of that, and I wanted to reread the message,
but it seems that I either never saved it or lost it during the
system moves I've made since then.
So...could someone dredge it up out of their archives and
post it, or just explain it once again for me?  I'd
be much obliged...

Adam