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