C -------  mpi_exch.F --------------------------------------- 29.11.01 ----
C                                                           (c) M.Pester
C -------------------------------------------------------------------------
C *******  EXCHNG : Austausch zweier (gleichlanger) Pakete zwischen 
C                   zwei Prozessoren
C  L     (I)  Linknummer, 1,...,NCUBE
C  N     (I)  Anzahl Worte zu senden / empfangen
C  XS    (I)  Send Buffer
C  XR    (O)  Recv Buffer
C
	SUBROUTINE EXCHNG(L,N,XS,XR)
	DIMENSION  XS(*),XR(*)
	LOGICAL  Btest
	INCLUDE 'include/trnet.inc'
	INCLUDE 'include/times.inc'
	INCLUDE 'mpif.h'
	INTEGER STATUS(MPI_STATUS_SIZE),IERROR
#ifdef SECNDS_EXTERNAL
        External secnds
#endif

	T0=secnds(0.0)
        Iwho = IEOR(ICH,ISHFT(1,L-1))
	CALL MPI_SENDRECV(XS,N,MPI_INTEGER,Iwho,19,
     +			  XR,N,MPI_INTEGER,Iwho,19,
     +			  MPI_COMM_WORLD, STATUS, IERROR)
	TSndRcv=TSndRcv+secnds(T0)
	Nout = Lsend
	RETURN
	END