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: combinators generalizations kernel math prettyprint ;
IN: rosetta-code.bearings
 
: delta-bearing ( x y -- z )
    swap - 360 mod {
        { [ dup 180 > ] [ 360 - ] }
        { [ dup -180 < ] [ 360 + ] }
        [ ]
    } cond ;
 
: bearings-demo ( -- )
    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
    [ delta-bearing . ] 2 12 mnapply ;
 
MAIN: bearings-demo