the angle of a straight line drawn between 2 points

Hi,

I need a function which computes the angle of a straight line drawn 
between 2 points.
It should give result in turns ( from 0 to 1 ).
I have made a function :


GiveTurn

and some tests for it.

It gives expected results. Can I as for an opinion of experts ?


TIA


Adam



==== code ==========================


kill(all);



/*
  Determines the angle of a straight line drawn between point one and two.
  The number returned, which is a double in degrees, tells us how much 
we have to rotate a horizontal line clockwise for it to match the line 
between the two points.
 
http://codeforeverything.wikidot.com/get-angle-of-line-between-two-points 

      */



GiveTurn(z3,z4):=(dx:realpart(z4)-realpart(z3),
     dy:imagpart(z4)-imagpart(z3),
     b:atan2(dy,dx),
     if (b<0) then b:b+2*%pi else b,
     float(b/(2*%pi)));



compile(all)$

GiveTurn(0, 1+0*%i);
GiveTurn(0, 1+1*%i);
GiveTurn(0, 0+1*%i);
GiveTurn(0,-1+1*%i);
GiveTurn(0,-1+0*%i);
GiveTurn(0,-1-1*%i);
GiveTurn(0, 0-1*%i);
GiveTurn(0, 1-1*%i);