code: def uniq2orderipix(uniq):
      
      order = ((np.log2(uniq//4)) // 2)
      order = order.astype(int)
      ipix = uniq - 4 * (4**order)
  
      return order, ipix
docs: convert a HEALPix pixel coded as a NUNIQ number
      to a (norder, ipix) tuple