1. A method of deriving at least one motion vector of a bi-predictive block by applying a bit operation, performed by a moving picture coding system, the method comprising: selecting, by the moving picture coding system, a list 0 motion vector of a co-located block in a first reference picture for the bi-predictive block as a motion vector for deriving motion vectors of the bi-predictive block regardless of whether the co-located block includes a list 1 motion vector if the co-located block includes the list 0 motion vector, the first reference picture being a type of reference picture permitted to be located temporally before a current picture when the first reference picture precedes the current picture and permitted to be located temporally after the current picture when the first reference picture follows the current picture, the current picture including the bi-predictive block; and deriving, by the moving picture coding system, at least one motion vector of the bi-predictive block by applying a bit operation to the selected motion vector.