Possible implementation of math.atan2 in Lua

function math.atan2(y, x)
    if x > 0 then -- regular case (first or fourth quadrants, the range of atan)
        return math.atan(y/x)
    elseif y >= 0 and x < 0 then -- second quadrant case
        return math.atan(y/x + math.pi)
    elseif y < 0 and x < 0 then -- third quadrant case
        return math.atan(y/x - math.pi)
    elseif y > 0 and x == 0 then -- pointing up
        return math.pi/2
    elseif y < 0 and x = 0 then -- pointing down
        return -math.pi/2
    else -- special quirk if y = 0 and x = 0
        return 0
    end
end