Decomposing Generalized Bent and Hyperbent Functions

In this paper, we introduce generalized hyperbent functions from F-2n to Z(2k), and investigate decompositions of generalized (hyper) bent functions. We show that generalized (hyper) bent functions f from F-2n to Z(2k) consist of components which are generalized (hyper) bent functions from F-2n to Z(2k)' for some k' < k. For even n, most notably we show that the g-hyperbentness of f is equivalent to the hyperbentness of the components of f with some conditions on the Walsh-Hadamard coefficients. For odd n, we show that the Boolean functions associated to a generalized bent function form an affine space of semibent functions. This complements a recent result for even n, where the associated Boolean functions are bent.