[@$3.1415rin]

that code snippet should be right if you assume every plane if going thru 0,0,0. Planes are normally specified with the normal and then with the distance to the origin of your coordinate system ( It's called hessesche form I guess ), but this'd be 0 in your case I guess. so two possible planes, first checking if the normal is right at all, so we know that the planes are identical. ( if you have 2 planes which are principally identical, but their calculation was different, you might still get problem due to rounding in float operations )

checking the dotproducts should then be ok, too