Quaternion rotation

[lastgen]

I know this isn't really a C++ question, but Quaternions are commonly used by many C++ coders so I'll ask this here... I am trying to rotate object A by the reverse of object B's orientation, where I know the orientations of each in quaternion form. I can do this by converting the quaternion B to a matrix and multiplying A by the inverse of Matrix B, but this seems like a waste or processing power. What other methods can I use to reverse the rotation of a Quaternion? Would negative scaling work? When I die I'd like to go peacefully in my sleep like my father, not screaming in terror like his passengers!!!