Cimmarusti, Andres D.Norris, David G.Patterson, Burkley D.Cahoon, EricOrozco, Luis A.gfncalc is a C++ program that calculates second order normalized correlation functions from raw photon arrival times. It can read trigger pulses from another device to implement filtering. It features a simple command-line interface and it is cross-platform.This program is fast at processing large datasets.en-USC++gfncalcphotonSoftware