Multiplying system based on the Booth's algorithm and generating a positive or negative product in response to a mode signal

摘要

A multiplying system based on the Booth's algorithm, comprises a Booth's decoder having a first input receiving a multiplier "Y" and a second input receiving a mode signal designating either a first multiplication of "X×Y" (where "X" is a multiplicand) or a second multiplication of "-X×Y". The Booth's decoder generates a Booth's decoded value and a sign selection signal to a partial product generation circuit which also receives the multiplicand "X", so that the partial product generation circuit generates either a first partial product of "X. times.Y" or a second partial product of "-X×Y" in accordance with the sign selection signal. An output of the partial product generation circuit is summed by a partial product summing circuit, and an output of the partial product summing circuit is added to a value "A" stored in an output register by an arithmetic unit. Thus, the accumulating multiplication "A=A.+-.X×Y" can be executed in the same hardware without using a circuit for sign-inverting the output of the partial product summing circuit.