anchor.diff:    integer(bit_kind), intent(in)  :: key2(Nint,2)
     integer, intent(out)           :: idx(0:sze)
     
  -  integer                        :: i,l
  +  integer                        :: i,l,m
     integer                        :: degree_x2
   
     ASSERT (Nint > 0)
  
positive.code:      do i=1,sze
         degree_x2 = 0
         !DEC$ LOOP COUNT MIN(4)
         do l=1,Nint
           degree_x2 = degree_x2+ popcnt(xor( key1(l,1,i), key2(l,1))) +&
               popcnt(xor( key1(l,2,i), key2(l,2)))
           if (degree_x2 > 4) then
             exit
           endif
  
negative.code:   degree = popcnt(xor( ref_bitmask(1,1), key2(1,1))) +                      &
        popcnt(xor( ref_bitmask(1,2), key2(1,2)))
    !DEC$ NOUNROLL
    do m=2,Nint
      degree = degree+ popcnt(xor( ref_bitmask(m,1), key2(m,1))) +            &
          popcnt(xor( ref_bitmask(m,2), key2(m,2)))
    enddo
    degree = ishft(degree,-1)
    
  