bitmasks
  N_int         integer
  bit_kind      integer
  N_mask_gen    integer
  generators    integer*8 (bitmasks_N_int*bitmasks_bit_kind/8,2,6,bitmasks_N_mask_gen)
  N_mask_cas    integer
  cas           integer*8 (bitmasks_N_int*bitmasks_bit_kind/8,2,bitmasks_N_mask_cas)