  The subset sum problem over finite fields is a well-known {\bf NP}-complete
problem. It arises naturally from decoding generalized Reed-Solomon codes. In
this paper, we study the number of solutions of the subset sum problem from a
mathematical point of view. In several interesting cases, we obtain explicit or
asymptotic formulas for the solution number. As a consequence, we obtain some
results on the decoding problem of Reed-Solomon codes.
