This article considers the methods of calculating the cross-correlation function in determining the disparity from the images of a stereo pair formed by a stereo vision system. When determining the disparity, it is necessary to find a point on the second image of the stereo pair at a given point of the first image, which can be done by finding the maximum of the cross-correlation function. The possibility of reducing the amount of calculations in the time domain when using a non-positional calculus system, also called a residue number system, is considered. As a result of modeling based on a system of positional calculus and a residue number system using similar-shaped functions shifted along the X axis relative to each other, as well as using real stereo images, the coincidence of the main maxima of the cross-correlation function is shown with a significant reduction in the amount of calculations.