Arithmetic logic unit having plural independent sections and register

Abstract

An arithmetic logic unit (230) may be divided into a plurality of independent sections (301, 302, 303, 340). A bit zero of carry status signal corresponding to each section that is stored in a flags register (211), which preferably includes more bits than the maximum number of sections of the arithmetic logic unit (230). New status signals may overwrite the previous status signals or rotate the stored bits and store the new status signals. A status register (210) stores a size indicator that determines the a number of sections of the arithmetic logic unit (230). A status detector has a zero detector (321, 322, 323, 324) for each elementary section (301, 302, 303, 304) of the arithmetic logic unit (230). When there are fewer than the maximum number of sections, these zero signals are ANDed (331, 332, 341). A multiplexer couples the carry-out of an elementary (311, 312, 313, 314) to the carry-in of an adjacent elementary section (301, 302, 303, 304) or not depending on the selected number of sections. The status detector supplies carry outs from each elementary section (301, 302, 303, 304) not coupled to an adjacent elementary section (301, 302, 303, 304) to the flags register (211). Status signals stored in the flags register (211) influence the combination of inputs formed by the arithmetic logic unit (230) within corresponding sections. An expand circuit (238) expands selected bits of flags register (211) to form a third input to a three input arithmetic logic unit (230).