mul8
        asl a                   ; 2
        rol a                   ; 2
        rol a                   ; 2
        tax                     ; 2 - use X as temp
        and #%11111000          ; 2
        pha                     ; 3 - final A value
        txa                     ; 2 - get temp from X
        rol a                   ; 2 - shift once more to get proper MSB
        and #%00000111          ; 2
        tax                     ; 2
        pla                     ; 3
        rts                     ; -- +
                                ; 24 cycles (excl. jsr/rts)
                                ; 13 bytes (excl. rts)