SUBROUTINE swap_timelevel

!------------------------------------------------------------------------------!
! Actual revisions:
! -----------------
! Swaping of salinity
!
! Former revisions:
! -----------------
! $Id: swap_timelevel.f90 95 2007-06-02 16:48:38Z raasch $
!
! 75 2007-03-22 09:54:05Z raasch
! moisture renamed humidity
!
! 19 2007-02-23 04:53:48Z raasch
! Swaping of top fluxes
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.8  2004/01/28 15:28:18  raasch
! Swaping for Runge-Kutta schemes implemented
!
! Revision 1.1  2000/01/10  10:08:58  10:08:58  raasch (Siegfried Raasch)
! Initial revision
! 
!
! Description:
! ------------
! Swap of timelevels of variables after each timestep
!------------------------------------------------------------------------------!

    USE arrays_3d
    USE cpulog
    USE interfaces
    USE control_parameters

    IMPLICIT NONE


    CALL cpu_log( log_point(28), 'swap_timelevel', 'start' )

!
!-- Incrementing timestep counter
    timestep_count = timestep_count + 1

!
!-- Swap of 3-level variables
    IF ( timestep_scheme(1:5) /= 'runge' )  THEN

       SELECT CASE ( MOD( timestep_count, 3 ) )

          CASE ( 0 )

             u_m  => u_1;   u  => u_2;  u_p  => u_3
             v_m  => v_1;   v  => v_2;  v_p  => v_3
             w_m  => w_1;   w  => w_2;  w_p  => w_3
             pt_m => pt_1;  pt => pt_2; pt_p => pt_3
             IF ( .NOT. constant_diffusion )  THEN
                e_m => e_1;  e => e_2;  e_p => e_3
             ENDIF
             IF ( humidity  .OR.  passive_scalar )  THEN
                q_m => q_1;  q => q_2;  q_p => q_3
             ENDIF

          CASE ( 1 )

             u_m  => u_2;   u  => u_3;  u_p  => u_1
             v_m  => v_2;   v  => v_3;  v_p  => v_1
             w_m  => w_2;   w  => w_3;  w_p  => w_1
             pt_m => pt_2;  pt => pt_3; pt_p => pt_1
             IF ( .NOT. constant_diffusion )  THEN
                e_m => e_2;  e => e_3;  e_p => e_1
             ENDIF
             IF ( humidity  .OR.  passive_scalar )  THEN
                q_m => q_2;  q => q_3;  q_p => q_1
             ENDIF

          CASE ( 2 )

             u_m  => u_3;   u  => u_1;  u_p  => u_2
             v_m  => v_3;   v  => v_1;  v_p  => v_2
             w_m  => w_3;   w  => w_1;  w_p  => w_2
             pt_m => pt_3;  pt => pt_1; pt_p => pt_2
             IF ( .NOT. constant_diffusion )  THEN
                e_m => e_3;  e => e_1;  e_p => e_2
             ENDIF
             IF ( humidity  .OR.  passive_scalar )  THEN
                q_m => q_3;  q => q_1;  q_p => q_2
             ENDIF

       END SELECT

    ENDIF

!
!-- Swap of 2-level variables
    SELECT CASE ( MOD( timestep_count, 2 ) )

       CASE ( 0 )

          IF ( timestep_scheme(1:5) == 'runge' )  THEN

             u  => u_1;   u_p  => u_2
             v  => v_1;   v_p  => v_2
             w  => w_1;   w_p  => w_2
             pt => pt_1;  pt_p => pt_2
             IF ( .NOT. constant_diffusion )  THEN
                e => e_1;    e_p => e_2
             ENDIF
             IF ( ocean )  THEN
                sa => sa_1;  sa_p => sa_2
             ENDIF
             IF ( humidity  .OR.  passive_scalar )  THEN
                q => q_1;    q_p => q_2
             ENDIF

          ELSE
!
!--          Old timelevels are needed for explicit diffusion within leapfrog
             IF ( .NOT. constant_diffusion )  THEN
                kh_m => kh_1;  kh => kh_2
                km_m => km_1;  km => km_2
                IF ( use_surface_fluxes )  THEN
                   usws_m => usws_1;  usws => usws_2
                   vsws_m => vsws_1;  vsws => vsws_2
                   shf_m  => shf_1;   shf  => shf_2
                   IF ( humidity  .OR.  passive_scalar )  THEN
                      qsws_m => qsws_1;  qsws => qsws_2
                   ENDIF
                ENDIF
                IF ( prandtl_layer )  THEN
                   rif_m  => rif_1;   rif  => rif_2
                ENDIF
                IF ( use_top_fluxes )  THEN
                   tswst_m => tswst_1;  tswst => tswst_2
                   IF ( humidity  .OR.  passive_scalar )  THEN
                      qswst_m => qswst_1;  qswst => qswst_2
                   ENDIF
                ENDIF
             ENDIF

             IF ( humidity )  THEN
                vpt_m => vpt_1;  vpt => vpt_2
             ENDIF

          ENDIF

       CASE ( 1 )

          IF ( timestep_scheme(1:5) == 'runge' )  THEN

             u  => u_2;   u_p  => u_1
             v  => v_2;   v_p  => v_1
             w  => w_2;   w_p  => w_1
             pt => pt_2;  pt_p => pt_1
             IF ( .NOT. constant_diffusion )  THEN
                e => e_2;    e_p => e_1
             ENDIF
             IF ( ocean )  THEN
                sa => sa_2;  sa_p => sa_1
             ENDIF
             IF ( humidity  .OR.  passive_scalar )  THEN
                q => q_2;    q_p => q_1
             ENDIF

          ELSE

             IF ( .NOT. constant_diffusion )  THEN
                kh_m => kh_2;  kh => kh_1
                km_m => km_2;  km => km_1
                IF ( use_surface_fluxes )  THEN
                   usws_m => usws_2;  usws => usws_1
                   vsws_m => vsws_2;  vsws => vsws_1
                   shf_m  => shf_2;   shf  => shf_1
                   IF ( humidity  .OR.  passive_scalar )  THEN
                      qsws_m => qsws_2;  qsws => qsws_1
                   ENDIF
                ENDIF
                IF ( prandtl_layer )  THEN
                   rif_m  => rif_2;   rif  => rif_1
                ENDIF
                IF ( use_top_fluxes )  THEN
                   tswst_m  => tswst_2;  tswst => tswst_1
                   IF ( humidity  .OR.  passive_scalar )  THEN
                      qswst_m => qswst_2;  qswst => qswst_1
                   ENDIF
                ENDIF
             ENDIF

             IF ( humidity )  THEN
                vpt_m => vpt_2;  vpt => vpt_1
             ENDIF

          ENDIF

    END SELECT

    CALL cpu_log( log_point(28), 'swap_timelevel', 'stop' )

 END SUBROUTINE swap_timelevel