A path metric difference computation unit is disclosed for computing path differences through a multiple-step trellis. Path differences are computed between paths through a multiple-step trellis, wherein a first path is a winning path for each single-step-trellis period of a multiple-step-trellis cycle, a second path is a winning path for a first single-step-trellis period and is a losing path for a second single-step-trellis period and a third path is a losing path for a first single-step-trellis period and is a winning path for a second single-step-trellis period. The disclosed path metric difference computation unit comprises path metric difference generators for generating a path metric difference Δ0 for a second single-step-trellis period based on a difference between the first path and the second path, and a path metric difference Δ−1 for a first single-step-trellis period based on a difference between the first path and the third path, wherein intermediate path metric values or intermediate path metric difference values are reused to generate the path metric differences Δ0 or Δ−1.