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In this letter, numerically efficient implementation of the finite-difference time domain (FDTD)-compatible Green's function on a multicore processor is presented. Recently, closed-form expression of this discrete Green's function (DGF) was derived, which simplifies its application in the FDTD simulations of radiation and scattering problems. Unfortunately, the new DGF expression involves binomial coefficients, whose computations may cause long runtimes and numerical problems. The proposed fast implementation of the DGF is based on the multiple precision arithmetic and employs a common programming language extended with the OpenMP parallel programming interface. As a result, the speedup factor of three orders of magnitude compared to the previous implementation was obtained, thus applicability of the DGF in FDTD simulations was significantly improved.