Low density parity check (LDPC) decoding can be mapped to a class of DSP instructions called MINST. The MINST class of instructions significantly enhance the efficiency of LDPC decoding by merging several of the functions required by LDPC decoders into a single MINST instruction. This invention is an efficient implementation of the MINST class of instructions using a configurable three input arithmetic logic unit. The carry output results of the three input arithmetic logic unit enable permit boundary decisions in a range determination required by the MINST instruction. The preferred embodiment employs 2's complement arithmetic and carry-save adder logic. This invention allows reuse of hardware required to implement MAX* functions in LDPC functions.