Point density falloff

This seems a bit basic, so I’ll start by saying I did try searching for it, but I have evidently failed to find what I am after.

Does anyone know the actual functions used by the various falloff options for the point density texture type?

I am currently doing some scientific visualization stuff, and I am specifically after a 1/distance^2 falloff. Looking at them the ‘soft’ option with its default value of 2 looks right, and indeed based on playing with its values I suspect its function is 1/distance^[softness parameter]. Anyone got anything beyond my guesses?