SUBROUTINE swap_timelevel

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! PALM is free software: you can redistribute it and/or modify it under the terms
! of the GNU General Public License as published by the Free Software Foundation,
! either version 3 of the License, or (at your option) any later version.
!
! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License along with
! PALM. If not, see <http://www.gnu.org/licenses/>.
!
! Copyright 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
!
! 
! Former revisions:
! -----------------
! $Id: swap_timelevel.f90 1116 2013-03-26 18:49:55Z witha $
!
! 1115 2013-03-26 18:16:16Z hoffmann
! calculation of qr and nr is restricted to precipitation
!
! 1111 2013-03-08 23:54:10Z raasch
! openACC directives added
!
! 1053 2012-11-13 17:11:03Z hoffmann
! swap of timelevels for nr, qr added
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 1032 2012-10-21 13:03:21Z letzel
! save memory by not allocating pt_2 in case of neutral = .T.
!
! 1010 2012-09-20 07:59:54Z raasch
! cpp switch __nopointer added for pointer free version
!
! 1001 2012-09-13 14:08:46Z raasch
! all actions concerning leapfrog scheme removed
!
! 102 2007-07-27 09:09:17Z raasch
! swaping of uswst, vswst included
!
! 95 2007-06-02 16:48:38Z raasch
! Swaping of salinity
!
! 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

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

!
!-- Swap of variables
#if defined( __nopointer )
    CALL cpu_log( log_point(28), 'swap_timelevel (nop)', 'start' )

    !$acc kernels present( pt, pt_p, u, u_p, v, v_p, w, w_p )
    u  = u_p
    v  = v_p
    w  = w_p
    pt = pt_p
    !$acc end kernels
    IF ( .NOT. constant_diffusion )  THEN
       !$acc kernels present( e, e_p )
       e = e_p
       !$acc end kernels
    ENDIF
    IF ( ocean )  THEN
       sa = sa_p
    ENDIF
    IF ( humidity  .OR.  passive_scalar )  THEN
       q = q_p             
       IF ( cloud_physics  .AND.  icloud_scheme == 0 )  THEN
          qr = qr_p
          nr = nr_p
       ENDIF
    ENDIF

    CALL cpu_log( log_point(28), 'swap_timelevel (nop)', 'stop' )
#else
    CALL cpu_log( log_point(28), 'swap_timelevel', 'start' )

    SELECT CASE ( MOD( timestep_count, 2 ) )

       CASE ( 0 )

          u  => u_1;   u_p  => u_2
          v  => v_1;   v_p  => v_2
          w  => w_1;   w_p  => w_2
          IF ( .NOT. neutral )  THEN
             pt => pt_1;  pt_p => pt_2
          ENDIF
          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
             IF ( cloud_physics  .AND.  icloud_scheme == 0  .AND.  &
                  precipitation )  THEN
                qr => qr_1;    qr_p => qr_2
                nr => nr_1;    nr_p => nr_2
             ENDIF
          ENDIF


       CASE ( 1 )

          u  => u_2;   u_p  => u_1
          v  => v_2;   v_p  => v_1
          w  => w_2;   w_p  => w_1
          IF ( .NOT. neutral )  THEN
             pt => pt_2;  pt_p => pt_1
          ENDIF
          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
             IF ( cloud_physics  .AND.  icloud_scheme == 0  .AND.  &
                  precipitation)  THEN
                qr => qr_2;    qr_p => qr_1
                nr => nr_2;    nr_p => nr_1
             ENDIF
          ENDIF


    END SELECT

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

 END SUBROUTINE swap_timelevel