module dottest {
  logical, parameter, private ::  T = .true.,  F = .false.
contains
  subroutine dot_test( oper, n_mod, n_dat, dot1, dot2) {
    integer,             intent (in)  :: n_mod, n_dat 
    real, dimension (2), intent (out) :: dot1, dot2
    interface {
       function oper( adj, add, mod, dat) result(stat) {
            integer              :: stat
            logical, intent (in) :: adj, add
            real, dimension (:)  :: mod, dat
            }
       }
    real, dimension( n_mod)           :: mod1, mod2
    real, dimension( n_dat)           :: dat1, dat2
    integer                           :: stat
    call random_number( mod1);  call random_number( dat2)
    stat = oper( F, F, mod1, dat1);  dot1( 1) = dot_product( dat1, dat2)
    stat = oper( T, F, mod2, dat2);  dot1( 2) = dot_product( mod1, mod2)
    write (0,*) dot1 
    stat = oper( F, T, mod1, dat1);  dot2( 1) = dot_product( dat1, dat2)
    stat = oper( T, T, mod2, dat2);  dot2( 2) = dot_product( mod1, mod2)
    write (0,*) dot2
  }
}