Cosmic-ray hadronic interaction matrices for gamma-ray and other secondaries for an interstellar medium target are available as described in Huang et al. Astroparticle Physics, 27, 429 (2007). These require significant effort in practice to compute emissivities for given input spectra. To supplement these matrices I provide here a C++ class which reads the matrices, interpolates on user-defined particle and gamma-ray energy grids, and computes the gamma-ray emissivity either differential...