qloglin
is simply the
quantile function
$$G^{-1}_\theta(u) = \theta^{-1} \log \Big( 1 + (e^\theta - 1)u \Big)$$
in this model, for $u \in [0,1]$. This quantile function is used for the computation of quantiles of $\widehat F_m$ in quantilesLogConDens
.qloglin(u, t)