IsLeapYear()

leap.c

#include <stdbool.h>
#include <assert.h>

/**
 * Modified version of https://stackoverflow.com/a/11595914/2566213
 * with 4000th check added.
 */
bool
IsLeapYear(const int y)
{
    return (
        ((y & 3) == 0) &&
        (
            (y % 25 != 0 ) ||
            (
                ((y & 15) == 0) &&
                (y % 4000 != 0)
            )
        )
    );
}

void
AssertIsLeapYear()
{
    assert(!IsLeapYear(1901));
    assert(!IsLeapYear(1903));
    assert(!IsLeapYear(1905));
    assert(IsLeapYear(1904));
    assert(IsLeapYear(1908));
    assert(IsLeapYear(1996));
    assert(IsLeapYear(2004));
    assert(!IsLeapYear(1700));
    assert(!IsLeapYear(1800));
    assert(!IsLeapYear(1900));
    assert(!IsLeapYear(2100));
    assert(IsLeapYear(1600));
    assert(IsLeapYear(2000));
    assert(IsLeapYear(2400));
    assert(IsLeapYear(3600));
    assert(IsLeapYear(4400));
    assert(!IsLeapYear(4000));
    assert(!IsLeapYear(8000));
}