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


var subtract = Fn.new { |b1, b2|
    var d = (b2 - b1) % 360
    if (d < -180)  d = d + 360
    if (d >= 180)  d = d - 360
    return (d * 10000).round / 10000 // to 4dp
}
 
var pairs = [
    [ 20,  45],
    [-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]
]
 
System.print("Differences (to 4dp) between these bearings:")
for (pair in pairs) {
    var p0 = pair[0]
    var p1 = pair[1]
    var diff = subtract.call(p0, p1)
    var offset = (p0 < 0) ? " " : "  "
    System.print("%(offset)%(p0) and %(p1) -> %(diff)")
}