private static boolean isLeapYear(int prolepticYear) {
        return ((prolepticYear & 3) == 0) && ((prolepticYear % 100) != 0 || (prolepticYear % 400) == 0);
    }
Checks if the year is a leap year, according to the ISO proleptic
calendar system rules.
indexr-common/src/main/java/io/indexr/util/DateTimeUtil.java