A method for forward error correction decoding. The method generally includes steps (A) to (D). Step (A) may calculate a plurality of metrics of a codeword using a forward error correction process on a trellis having a plurality of stages. Step (B) may update the metrics over each of the stages. Step (C) may permute the metrics in each of the stages. Step (D) may generate a signal carrying a plurality of decoded bits of the codeword.