1. A system for determining one or more state probabilities for one or more states in a trellis representation, the system comprising: branch metric logic for determining one or more branch metrics for one or more branches between one or more states in a first portion of the trellis and one or more states in a second portion of the trellis; and state probability logic for determining one or more state probabilities for one or more of the states, comprising: first logic for grouping one or more of the branches into groups; second logic for performing, for one or more of the groups, a first group operation on one or more of the branch metrics for the branches in the group to determine a group value for the group; third logic for updating, for one or more of the groups, the group value for the group based on one or more previously determined state probabilities; and fourth logic for performing, for one or more of the states, a second group operation on one or more of the updated group values to determine a state probability for the state.