Systems and related methods are described for (1) determining one or more
state probabilities for one or more states in a trellis representation; (2) determining
an estimate of or extrinsic output for a bit using a trellis representation; (3)
performing a MAX* 2-1 operation; and (4) computing forward state probabilities
in a forward mode of operation and computing backward state probabilities in a
backward mode of operation. Combinations of the foregoing are also described.