Quadratic vector extrapolation

[realMakc]

Hi, I need to extrapolate vector v_1 from v0, v1 and v2 (see attached pic), so that if v2 is on the right/left (2D case for simplicity) of v1-v0, v_1 would also be on the right/left.

My initial solution was like this:
v2 - v1 = v1 - v0 + some dv,
v1 - v0 = v0 - v_1 + dv,
and from there
v_1 = 3(v0 - v1) + v2.

This, however, produces ugly results when abs (v2-v1) < abs (v1-v0) - point v_1 is placed very far from v0. So I need a better formula for this.

Any help?