def _octant_coord(octant, x0, y0, x, y):
    """Return symmetrically reflected coordinates for a given pair."""
    if octant == 7:
        return x0 + x, y0 + y
    elif octant == 0:
        return x0 + x, y0 - y
    elif octant == 4:
        return x0 - x, y0 + y
    elif octant == 3:
        return x0 - x, y0 - y
    elif octant == 6:
        return x0 + y, y0 + x
    elif octant == 1:
        return x0 + y, y0 - x
    elif octant == 5:
        return x0 - y, y0 + x
    elif octant == 2:
        return x0 - y, y0 - x
