FILL     a n b --        Fill n bytes at addr a with val b.
HERE     -- a            Push HERE's address
H@       -- a            HERE @
MOVE     a1 a2 u --      Copy u bytes from a1 to a2, starting
                         with a1, going up.
MOVE-    a1 a2 u --      Copy u bytes from a1 to a2, starting
                         with a1+u, going down.