code: protected int computeFernValue(float c_x, float c_y, float rectWidth , float rectHeight , TldFernDescription fern ) {
  
  		rectWidth -= 1;
  		rectHeight -= 1;
  
  		int desc = 0;
  		for( int i = 0; i < fern.pairs.length; i++ ) {
  			Point2D_F32 p_a = fern.pairs[i].a;
  			Point2D_F32 p_b = fern.pairs[i].b;
  
  			float valA = interpolate.get_fast(c_x + p_a.x * rectWidth, c_y + p_a.y * rectHeight);
  			float valB = interpolate.get_fast(c_x + p_b.x * rectWidth, c_y + p_b.y * rectHeight);
  
  			desc *= 2;
  
  			if( valA < valB ) {
  				desc += 1;
  			}
  		}
  
  		return desc;
  	}
docs: Computes the value of the specified fern at the specified location in the image.