assembler conditional

  00DE                18     IXLENGTH equ 222;
                      19     
                      20     
                      21     $IF ((LOW IXLENGTH) = 0 )
0000 7E00             22             mov     r6,#HIGH IXLENGTH
                      23     $ELSE
                                     mov     r6,#((HIGH IXLENGTH) +1)
                             $ENDIF
                      26     
                      27     
  0100                28     XLENGTH equ 256;
                      29     
                      30     
                      31     $IF ((LOW XLENGTH) = 0 )
0002 7E01             32             mov     r6,#HIGH XLENGTH
                      33     $ELSE
                                     mov     r6,#((HIGH XLENGTH) +1)
                             $ENDIF