Return the start index of the pattern inside the input string in a
        Bitvector representation, otherwise it returns -1 (always using a BitVector)

        :param bitlength: size of the biitvector holding the result

def indexOf(self, pattern, start_idx, bitlength):
        """
        Return the start index of the pattern inside the input string in a
        Bitvector representation, otherwise it returns -1 (always using a BitVector)

        :param bitlength: size of the biitvector holding the result
        """
        return StrIndexOf(self, pattern, start_idx, bitlength)