Three input arithmetic logic unit capable of performing all possible

Abstract

A data processing apparatus includes a three input arithmetic logic unit (230) that generates a Boolean combination of the three inputs that is selected by a function signal. The arithmetic logic unit is capable of forming all possible Boolean combinations of the three inputs. Data registers (200) store the three data inputs and the arithmetic logic unit output. The second input signal comes from a controllable shifter (235). The shift amount is a default shift amount stored in a special data register, a predetermined set of bits of data recalled from a data register or zero. A one's constant source (236) is connected to the shifter (235) to supply an N bit digital signal of '1'. This permits generating a second input signal of the form 2.sup.N, with N being the shift amount. The output of the shifter (235) may be stored independently of the arithmetic logic unit (230) result. The third input signal comes from a multiplexer (233) that selects between an instruction specified immediate field, data recalled from a data register or a mask input from a mask generator (239). This mask input signal may be the default shift amount or a predetermined number of the least significant bits of a third input signal as selected by a multiplexer. In the preferred embodiment of this invention, the three input arithmetic logic unit (230) is embodied in a data processor circuits as a part of a multiprocessor integrated circuit (100) used in image processing.