def int2uint64(value):
    """
    Convert a signed 64 bits integer into an unsigned 64 bits integer.

    >>> print(int2uint64(1))
    1
    >>> print(int2uint64(2**64 + 1))  # ignore bits larger than 64 bits
    1
    >>> print(int2uint64(-1))
    18446744073709551615
    >>> print(int2uint64(-2))
    18446744073709551614
    """
    return value & 18446744073709551615
