'Handle "pseudo-unsigned" integers, if the user requested it.  Returns
the converted data array if so; otherwise returns None.
In this case case, we don\'t need to handle BLANK to convert it to NAN,
since we can\'t do NaNs with integers, anyway, i.e. the user is
responsible for managing blanks.'

def _convert_pseudo_unsigned(self, data):

    dtype = self._dtype_for_bitpix()
    if ((dtype is not None) and (dtype.kind == 'u')):
        bits = (dtype.itemsize * 8)
        data = np.array(data, dtype=dtype)
        data -= np.uint64((1 << (bits - 1)))
        return data
