Low-density parity check (LDPC) codes are used for forward error correction in several state-of-the-art and upcoming communications standards. This paper presents a new interleaver architecture for LDPC decoders, especially suitable for multi-mode codes such as IEEE 802.16e (WiMAX) and IEEE 802.11n (Wi-Fi), that utilizes a bidirectional datapath and shuffle network composed of transmission gates. An implementation of this architecture for IEEE 802.11n achieves 28% area reduction and similar throughput compared to a unidirectional reference design.