Faster leap year code. - Printable Version

Code:
  ! push eax          'for pseudo MOD, dividend and quotient

  ! mov FebDays, 28&  'not a leap year pre-set

  ! mov eax, 3???

  ! and eax, Year    'conditionally equivalent MOD 4

  ! jz MOD100        '0 is possible leap year

  ! jmp Done

  MOD100:

  ! push ebx          'for divisor

  ! push edx          'for high part of dividend, remainder (MOD)

  ! xor edx, edx

  ! mov eax, Year

  ! mov ebx, 100???

  ! div ebx

  ! cmp edx, 0???    'does MOD 100 = 0 ?

  ! pop edx

  ! pop ebx

  ! jz MOD400        '0 is possibly not a leap year

  ! jmp Is29Days      'non 0 is a leap year

  MOD400:

  ! and eax, 3???    'EAX has Year\100, so pseudo MOD 4 again

  ! jnz Done

  ! Is29Days:

  ! mov FebDays, 29&

  Done:

  ! pop eax '