  In this paper, the problem of constructing an efficient quantum circuit for
the implementation of an arbitrary quantum computation is addressed. To this
end, a basic block based on the cosine-sine decomposition method is suggested
which contains $l$ qubits. In addition, a previously proposed quantum-logic
synthesis method based on quantum Shannon decomposition is recursively applied
to reach unitary gates over $l$ qubits. Then, the basic block is used and some
optimizations are applied to remove redundant gates. It is shown that the exact
value of $l$ affects the number of one-qubit and CNOT gates in the proposed
method. In comparison to the previous synthesis methods, the value of $l$ is
examined consequently to improve either the number of CNOT gates or the total
number of gates. The proposed approach is further analyzed by considering the
nearest neighbor limitation. According to our evaluation, the number of CNOT
gates is increased by at most a factor of $\frac{5}{3}$ if the nearest neighbor
interaction is applied.
