On Wed, Feb 6, 2013 at 8:43 PM, <[email protected]> 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? Regards Haojian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
