meanshift strange for loop

edit

hy, what is this doing in imgproc/src/segmentation.cpp ?

for( i = 1; i < size1.height-1; i++, dptr += dstep - (size1.width-2)*3, mask += mstep*2 )
{  for( j = 1; j < size1.width-1; j++, dptr += cn )
   {
    int c0 = dptr[0], c1 = dptr[1], c2 = dptr[2];
    mask[j*2 - 1] = cdiff(-3) || cdiff(3) || cdiff(-dstep-3) || cdiff(-dstep) ||
    cdiff(-dstep+3) || cdiff(dstep-3) || cdiff(dstep) || cdiff(dstep+3);
   }
}