`On 02/06/2013 06:00 AM, Haojian Zhuang wrote:> On Wed, Feb 6, 2013 at 8:43 PM,  <jonghwa3.lee@samsung.com> wrote:>> On 2013년 02월 06일 20:42, Venu Byravarasu wrote:>>> By definition, leap year is one, which is a divisible by 4 & 400, excluding multiples of 100s.>>> Hence I feel this patch is not correct.>>>> No, I think you might misunderstood the it's meaning. The former code checks>> whether if it is multiple of 4 or not. Formal mathematical way to verify multiple of 4>> is just checks the last two digits are multiple of 4. This '(!year % 4) && (year % 100)'>> part does it. But with only that checking, it may miss the case of multiple of 400 which>> is also multiple of 4. Then my modification checks in hexadecimal, whether if number>> has any of 1st and 2nd bit with value 1. Because any number which has all bits above>> the 3rd can be divided with 4(2^2).>> (e.g. 44(0b101100) = 2^5+2^3+2^2 = 2^2(2^3 + 2 + 1))>> So It does same things with less instructions.> > I still can't understand your logic.> > Please check whether 200 year is leap year.> > 200(decimal) = 2b11001000> > !(200 & 0x3) = 1 (Your condition said that 200 year is a leap year.)> > According to this logic in below.>  if year mod 4 = 0 and year mod 100 <> 0 or year mod 400 = 0, then> it's a leap year.> > This tells us that 200 year isn't a leap year because 200 mod 100 ==> 0. So who is wrong?The rule is: it's a leap year if divisible by 4, unless it's divisibleby 100, but actually also including years divisible by 400. So, thecurrent code is correct, and the patch is wrong.http://en.wikipedia.org/wiki/Leap_year#Algorithm--To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at  http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at  http://www.tux.org/lkml/`