def solution(start, length):
    checksum = 0
    for i in range(length):
        base = start + length * i
        checksum ^= calc_checksum_range(base, base + length - i)
    return checksum

# P = [01]*
# P^P = 0
# P00^P01^P10^P11 = 0
def calc_checksum_range(_from, _to): # _from included, _to is NOT included
    checksum = 0
    remain = (-_from) % 4
    for i in range(_from, min(_from + remain, _to)):
        checksum ^= i
    checkpoint = _from + remain

    remain = _to % 4
    for i in range(max(_from, checkpoint, _to - remain), _to):
        checksum ^= i

    return checksum

tests = [
        ([0, 3], 2),
        ([17, 4], 14)
        ]

for i, o in tests:
    result = solution(*i)
    print (i, result == o, result, o)