Bias changes the "central tendency"/"hinge point" of the curve.

float GetBias(float t, float b) {  return (t / ((((1/b) - 2)*(1 - t))+1.0));}

Gain changes how rapidly we reach the bias point.

function GetGain(t,g) {  if(t < 0.5)    return GetBias(t * 2.0,g)/2.0;  else    return GetBias(t * 2.0 - 1.0,1.0 - g)/2.0 + 0.5;}