Levels... adjustment: what interpolation between white/black points and gray point?

[Peter1]

I' like to ask what interpolation is used, in the Levels adjustment, between the "white" and the "gray" output point, and the "gray" and the "black" output point? Is it linear interpolation or a curvy,  smooth interpolation like in the Curves adjustment? ( the question is also inspired by the Curves+ adjustment, where there is choice?)

Thanks

 

the question is related to the recent discussion here:

 

Edited May 11, 2022 by Peter1
title clarified