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


using Printf
 
function angdiff(a, b)
    r = (b - a) % 360.0
    if r ≥ 180.0
        r -= 360.0
    end
 
    return r
end
 
println("Input in -180 to +180 range:")
for (a, b) in [(20.0, 45.0), (-45.0, 45.0), (-85.0, 90.0), (-95.0, 90.0), (-45.0, 125.0), (-45.0, 145.0),
    (-45.0, 125.0), (-45.0, 145.0), (29.4803, -88.6381), (-78.3251, -159.036)]
    @printf("% 6.1f - % 6.1f = % 6.1f\n", a, b, angdiff(a, b))
end
 
println("\nInput in wider range:")
for (a, b) in [(-70099.74233810938, 29840.67437876723), (-165313.6666297357, 33693.9894517456),
    (1174.8380510598456, -154146.66490124757), (60175.77306795546, 42213.07192354373)]
    @printf("% 9.1f - % 9.1f = % 6.1f\n", a, b, angdiff(a, b))
end