(address, align)
return address & ~(align-1)
round_down(address, align) -> int

    Round down ``address`` to the nearest increment of ``align``.
round_down(address, align) -> int
round_down ( address align ) - > int
def round_down(address, align):
    """round_down(address, align) -> int

    Round down ``address`` to the nearest increment of ``align``.
    """
    return address & ~(align-1)
def round_down ( address , align ) : return address & ~ ( align - 1 )