Finding the angle between two bearings is often confusing.[1]



Task

Find the angle which is the result of the subtraction b2 - b1, where b1 and b2 are the bearings.


Input bearings are expressed in the range   -180   to   +180   degrees.

The  result  is also expressed in the range   -180   to   +180   degrees.



Compute the angle for the following pairs:

 20 degrees (b1) and 45 degrees (b2)
 -45 and 45
 -85 and 90
 -95 and 90
 -45 and 125
 -45 and 145
 29.4803 and -88.6381
 -78.3251 and -159.036


Optional extra
 
Allow the input bearings to be any (finite) value.



Test cases

 -70099.74233810938 and 29840.67437876723
 -165313.6666297357 and 33693.9894517456
 1174.8380510598456 and -154146.66490124757
 60175.77306795546 and 42213.07192354373


func angleDifference(a1: Double, a2: Double) -> Double {
  let diff = (a2 - a1).truncatingRemainder(dividingBy: 360)
 
  if diff < -180.0 {
    return 360.0 + diff
  } else if diff > 180.0 {
    return -360.0 + diff
  } else {
    return diff
  }
}
 
let testCases = [
  (20.0, 45.0),
  (-45, 45),
  (-85, 90),
  (-95, 90),
  (-45, 125),
  (-45, 145),
  (29.4803, -88.6381),
  (-78.3251, -159.036),
  (-70099.74233810938, 29840.67437876723),
  (-165313.6666297357, 33693.9894517456),
  (1174.8380510598456, -154146.66490124757),
  (60175.77306795546, 42213.07192354373)
]
 
print(testCases.map(angleDifference))