interpolate two angles

How can I interpolate two angles, is there an easy function?

eg:
angle 1 may be 320 degrees
angle 2 may be 20 degrees

of course the formula middle=(320+20)/2 is wrong, because the result would be 170, but it should be 350

...
while I write this, I already got an idea, something like

function findApproxAngle(a1#,a2#)
 ; find min and max
 min= a1
 if a2<min then min=a2
 max=a2
 if a1>max then max=a1 

 res#=0
 dist#=max-min
 if dist<=180 then
  res=(max+min)/2
 else
  res=(max+(((360-max)+min)/2.0)) mod 360.0
 endif
 return res#
end function

got to test this right now... :)

EDIT:
ehrm, Now I got a new problem: my "angles" use values from 0.0 to 1.0 and I have 4 of them that I want to use to create a middle value (well basicly its a hue value, not an angle, but it uses like an angle a closed circle)

So how could I do this? I thnik interpolating them one by one would not return a correct value ? And it would also be pretty slow.

Any ideas?