Patent ID: 8154973

Claim:
A reproduced signal evaluation method employed in a decoding operation, wherein the decoding operation uses a PRML method that decodes binarized bitstreams generated from reproduced signals obtained from an information-recorded medium, wherein the PRML method involves generating a plurality of evaluation bitstreams describing a state to which a current binarized bitstream will change, evaluating for each of the plurality of evaluation bitstreams a likelihood with which the current binarized bitstream will change to the evaluation bitstreams, determining the binarized bitstream after the state change and repeating the determination procedure to decode the reproduced signals; wherein the evaluation bitstreams are expressed as a combination of a main bitstream and sub bitstreams, the sub bitstreams being added to both of front and rear end of the main bitstream; wherein, in executing the decoding operation, the reproduced signal evaluation method generates a first evaluation bitstream corresponding to a most likely first state change and a second evaluation bitstream corresponding to a second most likely second state change; in generating a first evaluation bitstream and the second evaluation bitstream, prepares in advance a plurality of bit patterns describing the main bitstream; compares the main bitstreams and a part of the current binarized bitstream and selects from among the plurality of bit patterns a first main bitstream applicable to the first evaluation bitstream; executes an exclusive-OR calculation on the main bitstream applicable to the first evaluation bitstream to generate a second main bitstream applicable to the second evaluation bitstream; and attaching the sub bitstreams to the first main bitstream and the second main bitstream to generate the first evaluation bitstream and the second evaluation bitstream.