anchor.diff:          !       symmetrically.
           ! In/Out:
           !   rng: random number generator.
  +        !   qs: qmc_state_t derived type with information on
  +        !       current calculation. In/Out for compatibility with the
  +        !       Power-Pitzer excitation generators (not used for DMQMC).
           !   bloom_stats: information on blooms during calculation.
           !   spawn: stored information on spawning.
   
  
positive.code: 
          ! In:
          !   sys: information on system under consideration.
          !   qs: qmc_state_t derived type with information on
          !       current calculation.
          !   logging_info: information on current logging settings.
          !   weighted_sampling: stores sampling weights information when using
          !       importance sampling.
  
negative.code:         use spawn_data, only: spawn_t
  
          type(sys_t), intent(in) :: sys
          type(qmc_state_t), intent(inout) :: qs
          type(logging_t), intent(in) :: logging_info
          type(det_info_t), intent(in) :: cdet1, cdet2
          integer, intent(in) :: nattempts_current_det, ireplica
  