SetB:   ldrb    w3, [x0]
        and     w1, w1, 3           // value &= 3
        lsl     w1, w1, 1
        mov     w2, 6
        mvn     w2, w2
        and     w3, w3, w2          // B is cleared
        orr     w3, w3, w1
        strb    w3, [x0]
        ret