In this article, a novel simultaneous all-optical half-addition and half-subtraction scheme based on exploitation of cross-gain modulation (XGM) and four-wave mixing (FWM) in parametric medium consisting of As2Se3 chalcogenide HNLF capable of operating at 100Gbps bit rate has been demonstrated. The proposed scheme does not require any type of extra assist light sources. XGM & FWM processes have been utilized for the realization of borrow (AB‾ & A‾B) & carry (A.B) outputs, respectively of the proposed all-optical half-addition and half-subtraction module. The sum/difference output of proposed half-adder has been obtained by temporally combining earlier realized borrow (AB‾ & A‾B) signals. Q-factors and extinction ratios (ER) of over 10.5 & 11.3255dB, respectively for XGM based outputs (AB‾ & A‾B) and 10.73 & 17.47dB, respectively for FWM based outputs (A.B) have been achieved.