code: function sinsign(a, b, c) {
  
  			return (b[0] - a[0]) * (c[1] - a[1]) - (b[1] - a[1]) * (c[0] - a[0]);
  		}
docs: /* js/src/d2/pred/sinsign.js 
  Computes the cross product of vectors _ab_ and _ac_.
  Can be interpreted as the sinus sign in a "right-handed"
  coordinate system (i.e. clockwise angle values).
  sinsign(a, b, c) > 0 iff point c 'lies to the left' of segment _ab_.
  
  It also computes the area of the parallelogram defined by a, b
  and c. It can for example be used in the Quick Hull algorithm to find the
  farthest points from the pivot line.
  
  <p>
  Originally implemented as
  
  a[1] * (c[0] - b[0]) + b[1] * (a[0] - c[0]) + c[1] * (b[0] - a[0])
  
  with
  - 2 add
  - 3 sub
  - 3 mul
  
  Reduced to
  
  (b[0] - a[0]) * (c[1] - a[1]) - (b[1] - a[1]) * (c[0] - a[0])
  
  with
  - 5 sub
  - 2 mul