RAM LIST-DECODING OF NEAR CODEWORDS

Certain embodiments of the present invention are efficient run-time methods for creating and updating a RAM list of dominant trapping-set profiles for use in (LDPC) list decoding. A decoded correct codeword is compared to a near codeword to generate a new trapping-set profile, and the profile written to RAM. Record is kept of how many times RAM has been searched since a profile was last matched. Profiles that have not been matched within a specified number of searches are purge-eligible. Purge-eligible profiles are further ranked on other factors, e.g., number of times a profile has been matched since it was added, number of unsatisfied check nodes, number of erroneous bit nodes. If there is insufficient free space in RAM to store a newly-discovered profile, then purge-eligible profiles are deleted, beginning with the lowest-ranked profiles, until either (i) sufficient free space is created or (ii) there are no more purge-eligible profiles.