Question related to array slicing

In reply to poonamnlwd:
how to use array slicing for current_data. shifting bits from previous data to current data and current data will shift next and so on
array slicing is not working for data_from_one_row_2d[129:((2j)-1 -: 2)]}
getting error Range must be bounded by constant expressions


           data_out  = {prev_data[(2j)-1 -: 2],data_from_one_row_2d[129:((2j)-1 -: 2)]};