  We estimated the residual entropy of ice Ih by the recently developed
simulation protocol, namely, the combination of Replica-Exchange Wang-Landau
algorithm and Multicanonical Replica-Exchange Method. We employed a model with
the nearest neighbor interactions on the three-dimensional hexagonal lattice,
which satisfied the ice rules in the ground state. The results showed that our
estimate of the residual entropy is found to be within 0.038 % of series
expansion estimate by Nagle and within 0.000077 % of PEPS algorithm by
Vanderstraeten. In this article, we not only give our latest estimate of the
residual entropy of ice Ih but also discuss the importance of the uniformity of
a random number generator in MC simulations.
