scu 1130 in fig1 the first group of wires contributes t1 values to f1 the second group t2 values to f2 and the third group t3 values to f3 moreover s1 values of the wires in the first group s2 wire values in the second group and s3 wire values in the third group are also forwarded to the inner scu 1130 the sum s1 t1 can be larger than n1 meaning that some of the wire values may be needed in the corresponding arithmetic unit and may concurrently be forwarded to the inner scu 1130 the inner scu 1130 consists of simple comparators as one example the direct connections s1 s2 and s3 connected to inner scu 1130 may comprise a decoding of separate codes on lines n1 n2 and n3 producing by themselves a disconnected and thus undesirable comparator graph and the additional connections t1 t2 and t3 and functions f1 f2 and f3 provide to inner scu 1130 the additional information necessary to provide graph connection and enlarge the resulting fully detected subcode if the comparators in the inner scu 1130 are known in advance and if the structure of the arithmetic units is also known in advance then the code design problem can be accomplished using a procedure very similar to that outlined in fig4 as an example embodiment in accordance with the invention consider the case in which n1 1 n2 2 that f1 is a null operation so the value of wire 1.