A method for run-length encoding two or more data values, the method comprising: loading the data values into storage by forming a first data string, the data string comprising a plurality of data sub-strings and each data sub-string representing at least one of the data values; generating a second data string having a data sub-string corresponding to each data sub-string of the first data string, all the bits of each of the data sub-strings of the second data string having a first predetermined value if all the bits of the corresponding data sub-string of the first data string have a second predetermined value and having a third predetermined value if any of the bits of the corresponding data sub-string of the first data string has other than the second predetermined value; starting from a predetermined end of the second data string, counting the number of consecutive bits of the second data spring having the first predetermined value; and dividing the said number by the number of bits in each data sub-string.