God, just stop all this bullshit, it's getting ludicrous.

Here's the damn code (I dind't test it), make sure you understand it.
Code:
float p = ...; // blending percentage, range [0...1]


p = 0.5 - cos(p * 3.141592) / 2.0; // apply smooth falloff
vec_lerp(vPos_Output, vPos_Start, vPos_End, p);

POTATO-MAN saves the day! - Random