*The output is not yet multiplied to pi so that it is expressed in pi radians.
input: y = 1, x = 2
output: 0.1482 (correct)
input: y = -1, x = 2
output: -0.1482 (correct)
input: y = 1, x = -2
output: 0.8542 (even the sign is wrong)
input: y = -1, x=-2
output: -0.8518 (sign is again wrong and from my observation, it doesn't take into account the sign of x)