An approach to Boolean matching with respect to NPN operations, i.e. negation of the function, permutation of the inputs and negation of the inputs, is presented. The method is based on a canonical form defined in the Hadamard spectral domain. When applied to technology mapping, the idea is to keep the canonical function with each library cell, and to compute the canonical function for a subcircuit. The match is then accomplished using hashing on the canonical functions.