Task

Determine whether a given year is a leap year in the Gregorian calendar.



See also

 Leap year (wiki)


;Example
        move.l  #2018,d0
        bsr     leap_year
        addi.l  #28,d1      ; # days in February 2018
        rts
; Leap Year
;
; Input
;   d0=year
;
; Output
;   d1=1 if leap year, 0 if not leap year
;   zero flag clear if leap year, set if not
;
leap_year:
        cmpi.l  #1752,d0
        ble.s   not_leap_year
 
        move.l  d0,d1
        lsr.l   #1,d1
        bcs.s   not_leap_year
        lsr.l   #1,d1
        bcs.s   not_leap_year
 
; If we got here, year is divisible by 4.
        move.l  d0,d1
        divu    #100,d1
        swap    d1
        tst.w   d1
        bne.s   is_leap_year
 
; If we got here, year is divisible by 100.
        move.l  d0,d1
        divu    #400,d1
        swap    d1
        tst.w   d1
        bne.s   not_leap_year
 
is_leap_year:
        moveq.l #1,d1
        rts
not_leap_year:
        moveq.l #0,d1
        rts
 