Find if point lays on line segment

Question

I have line segment defined by two points A(x1,y1,z1) and B(x2,y2,z2) and point p(x,y,z). How can I check if the point lays on the line segment?

Answer 1

The cross product (B - A) × (p - A) should be much much shorter than B - A. Ideally, the cross product is zero, but that's unlikely on finite-precision floating-point hardware.