Leap year check using bitwise operators (amazing speed)

Question

Someone on JSPerf dropped an amazingly fast implementation for checking leap years of the ISO calendar (link: Odd bit manipulations):

function isLeapYear(yea         


        

Answer 1

If a number is divisible by 16 and divisible by 25, it's divisible by four times 25 (100) as well as 16 times 25 (400).