Dimensions of non-differentiability points of Cantor functions

For a probability vector (po,p1) there exists a corresponding self-similar Borel probability measure μ supported on the Cantor set C (with the strong separation property) in R generated by a contractive similitude h_i(x) = a_iX + b_i, i = 0,1. Let S denote the set of points of C at which the probability distribution function F(x) of μ, has no derivative, finite or infinite. The Hausdorff and packing dimensions of S have been found by several authors for the case that pi > d, i = 0,1. However, when po < ao (or equivalently p1 < a1) the structure of S changes significantly and the previous approaches fail to be effective any more. The present paper is devoted to determining the Hausdorff and packing dimensions of S for the case po < ao.