US Patent 7895507 Add-compare-select structures using 6-input lookup table architectures

An Add-Compare-Select circuit for use with a trellis decoder can include a first module and a second module. The first module can provide a difference signal specifying an indication of a difference between a second path cost and a first path cost of a trellis. The second path cost can be a sum of a second state cost and a second branch metric and the first path cost can be a sum of a first state cost and a first branch metric. The second module can select the first path cost or the second path cost as a new cost according to the difference signal of the first module.