borders types image in morphological operations

I perform different morphological operation and compare to cuda results in c++. anyone knows what padding done outside the image is it this types : 1) zero padding 2) mirror padding 3) constant padding

in image filter it is described but not in dilate erode https://www.mathworks.com/help/images/imfilter-boundary-padding-options.html example code

ImgTest=eye(10);
se1=ones(2);
ImgTestDilated=imdilate(ImgTest,se1);
ImgTestclosed=imerode(ImgTestDilated,se1);