Abstract: The invention discloses a signal decoding method for C3 decoding on a data storage medium. The data storage medium contains a lot of sectors, and each sector contains two C3 codes. Each C3 code contains a plurality of P codes and Q codes. The syndrome operation for an (N+1)th code and an error-correction for an N-th code are pipelined. An address for the (N+1)th code minus a predetermined value is an address for the N-th code.