BOOL point_in_triangle(point3d& a, point3d& b, point3d& c, point3d& cross){
  point3d vab, vac, vcrossa, vcrossb, vcrossc;
   
  sub_vectors(&vab.x, &b.x, &a.x);
  sub_vectors(&vac.x, &c.x, &a.x);

//  S triangle * 2;  
  point3d temp;
  cross_prod(&temp.x, &vab.x, &vac.x);
  double summa = vect_length(&temp.x);

  sub_vectors(&vcrossa.x, &a.x, &cross.x);
  sub_vectors(&vcrossb.x, &b.x, &cross.x);
  sub_vectors(&vcrossc.x, &c.x, &cross.x);
   
  double res_summa = 0.f;

// S a_b_cross * 2
  cross_prod(&temp.x, &vcrossa.x, &vcrossb.x);
  res_summa = vect_length(&temp.x);
  if(res_summa > summa){ return FALSE; }

// S c_b_cross * 2
  cross_prod(&temp.x, &vcrossb.x, &vcrossc.x);
  res_summa += vect_length(&temp.x);
  if(res_summa > summa){ return FALSE; }

// S a_c_cross * 2
  cross_prod(&temp.x, &vcrossa.x, &vcrossc.x);
  res_summa += vect_length(&temp.x);

  if(res_summa > (summa + summa * 0.0002)){ return FALSE; }

  return TRUE;
}