The adder/subtractor has a feedback loop in the parallel
sorter. It consists of 15 gates and cannot be divided into shorter
segments without slowing down the addition/subtraction. The
other decoder units have been designed such that the critical
path is not longer. Hence, the critical path of the overall decoder
has 15 gates. On application-specific integrated circuit (ASIC)
devices, a clock frequency of 150 MHz can be easily achieved.
From Fig. 6, it can be derived that the decoding for the (837,
726) code with 15 iterations takes