Parity prediction for binary adders with selection

摘要

An apparatus for predicting parity of a result produced by selection of the most or least significant thirty-two bits produced by a thirty-four bit adder, the parity being predicted concurrently with and independently of the result. Parity for byte Si of the selected result is derived by circuitry implementing the relationship:Pi = yP(M,n-1) V P(n,M+7) V y′P(M+8, n+7)in which Pi is the parity bit for Si, y is the positive sense of a signal indicating selection, of the most significant thirty-two result bits, y′ is the complement of y and indicates selection of the least significant thirty-­two result bits, P(M,n-1) is parity over the two most significant result bits in the portion of the result covering result bits m through n+7, P(m+8, n+7) is parity of the two least significant bits of the result portion, P(n, m+7) is parity over the central bits of the portion, i is an integer and 0≦i≦3, m=8i, and n=m+2.