A reliability unit is provided for determining a reliability value for at least one bit decision. The disclosed reliability unit comprises one or more functional elements, wherein each of the functional elements comprises at least four functional units and at least two registers, wherein each functional unit comprises a comparator and a multiplexer, and wherein an output of the comparator and an equivalence bit control the multiplexer. Generally, the reliability unit determines a reliability value for a bit decision associated with a maximum-likelihood path through a multiple-step trellis.