Calculates z-ordered values from x and y coordinates.

z_order.py

def z_order(x, y):
    """Creates a z-order value from the 15 least significant bits of
    the `int`s `x` and `y`.
    
    http://en.wikipedia.org/wiki/Z-order_curve
    """
    z = 0
    for bit_pos in range(15):
        z |= (x & (1 << bit_pos)) << bit_pos
        z |= (y & (1 << bit_pos)) << (bit_pos + 1)
    return z


if __name__ == '__main__':
    def test(x, y, z):
        assert z_order(x, y) == z, \
               "Expected %s, got %s." % (bin(z), bin(z_order(x, y)))
    test(0b0, 0b0, 0b0)
    test(0b1, 0b1, 0b11)
    test(0b0, 0b1, 0b10)
    test(0b100, 0b001, 0b010010)
    test(0b1111, 0b1111, 0b11111111)
    test(0b1111, 0b0000, 0b01010101)