object wrapping around octtree

im currently writing an octtree; when objects exceed the boundries of it, i want them to wrap around to the opposite end of the octtree. my friend said this can be accomplished by moding each exceeding axis of the coord by the absolute value of the length of the quadtree on that axis. for example if the x axis exceeds the bounding box for the octtree, new_x = old_x % fabs ( octtree.xwidth ). thats terrible syntax but hopefully you get the idea. however since last time i checked you cant mod floats. before i start racking my brain on this i just thought i would see what you guys have to say. thanks, hans