  We develop a C++ package of the STOchastic LAttice Simulation (STOLAS) of
cosmic inflation. It performs the numerical lattice simulation in the
application of the stochastic-$\delta N$ formalism. STOLAS can directly compute
the three-dimensional map of the observable curvature perturbation without
estimating its statistical properties. In its application to two toy models of
inflation, chaotic inflation and Starobinsky's linear-potential inflation, we
confirm that STOLAS is well-consistent with the standard perturbation theory.
Furthermore, by introducing the importance sampling technique, we have success
in numerically sampling the current abundance of primordial black holes in a
non-perturbative way. The package is available at
https://github.com/STOchasticLAtticeSimulation/STOLAS_dist.
