In this paper we characterize the controllers which are possible solutions of a certain H infinity control design problem, The problem considered is the optimal robustness problem for (weighted) normalized coprime factor/gap metric uncertainty, which is the basis for the Glover-McFarlane H infinity loop-shaping design method, Given a plant P and a corresponding controller C, we ask if C can be obtained from the optimization procedure for some choice of weighting function. This paper considers single-input/single-output systems and gives necessary and sufficient conditions for optimality which involve right-half plane pole/zero counts and a certain winding number test based on the Nyquist diagram of PG, The results give a characterization of this class of H infinity-optimal designs in the language of classical control.