Abstract: Method and apparatus for processing on-line operands A, B and C to produce the arithmetic expression S=(A.times.B)+C. In general, the apparatus includes an input processing unit, an on-line multiplication unit, and an on-line serial addition unit. The input processing unit is sequentially introducing the digits of operands, A, B and C into the apparatus, where each digit is represented in a redundant binary number format. The multiplication unit multiplies the sequence of digits of the operands A and B to produce the n-th product digit p.sub.n of the product P=A.times.B, with the most significant digit p.sub.o being computed first. The on-line addition unit adds the n-th product digit to the n-th digit of on-line operand C, so as to produce the n-th digit s.sub.n of the arithmetic expression S=(A.times.B)+C, with the most significant digit s.sub.o being produced first.

Abstract: A dual path switch (DPS) circuit for interfacing between arithmetic elements of a computer for performing Fast Fourier Transforms. The ratio of power consumption to signal resolution is very low. The DPS has very high frequency resolution, and to conserve power, many of its registers are reset to a logic low status when they are not in use. The DPS includes a diagnostic system which, upon a hardware failure, identifies the faulty gate and specifies the nature of the fault. The diagnostic system also provides a fault signal for use in testing for the mean time between failures.