#ifdef SHMEM
      subroutine gisum(aaa,nnn,bb1)
#else
      subroutine gisum(aaa,nnn,bbb)
#endif

c     
c***********************************************************************
c     
c     dl_poly global summation subroutine for hypercube - MPI version
c     integer version
c     
c     copyright - daresbury laboratory 1992
c     author    - w. smith march 1992.
c     MPI version - t.forester may 1995
c     CPP version - w.smith may 1995
c     
c     $Author: psh $
c     $Date: 1998-11-26 12:09:39 +0100 (Thu, 26. Nov 1998) $
c     $Revision: 997 $
c     $State$
c
c***********************************************************************
c     
      
      implicit real*8 (a-h,o-z)
      include 'dl_params.inc'
#include "comms.inc"

#ifdef SHMEM

      integer aaa(nnn),bb1(nnn)
      integer barrier
      integer bbb
      common/shared/bbb(mxbuff)
#else
      integer aaa(nnn),bbb(nnn)

#endif
#ifdef MPI

      integer status(MPI_STATUS_SIZE)
#ifdef MPIU       
#define MPI_allreduce MPI_allreduce_
#endif

      call MPI_allreduce(aaa,bbb,nnn,MPI_INTEGER,
     x  MPI_SUM,MPI_COMM_WORLD,ierror)

        do i = 1,nnn
          aaa(i) = bbb(i)
        enddo

#else
#ifndef SERIAL
c     
c     identify node
      iii=mynode()

c     
c     pass data to neighbouring nodes
      kk=1

      call gsync()

      do k=1,nodedim()

         k0=iii/kk-2*(iii/(2*kk))
         if(k0.eq.0)then
            
            k1=kk+iii
#ifdef INTEL
            msg1=irecv(Igsum_tag1+k,bbb,Ilen*nnn)
            call csend(Igsum_tag2+k,aaa,Ilen*nnn,k1,0)
            call msgwait(msg1)
#endif
#ifdef PVM
            call csend(Igsum_tag1+k,aaa,Ilen*nnn,k1,0)
            call crecv(Igsum_tag2+k,bbb,Ilen*nnn)
#endif
#if SHMEM

            ibar=barrier()
            call shmem_put(bbb, aaa, nnn, k1)
            call shmem_udcflush()
            ibar=barrier()

#endif
c     
c     add data received to local array
         
           do i=1,nnn
            
              aaa(i)=aaa(i)+bbb(i)
            
           enddo

         else                   
            
            k2=iii-kk
#ifdef INTEL
            msg2=irecv(Igsum_tag2+k,bbb,Ilen*nnn)
            call csend(Igsum_tag1+k,aaa,Ilen*nnn,k2,0)
            call msgwait(msg2)
#endif
#ifdef PVM
            call csend(Igsum_tag2+k,aaa,Ilen*nnn,k2,0)
            call crecv(Igsum_tag1+k,bbb,Ilen*nnn)
#endif
#if SHMEM

            ibar=barrier()
            call shmem_put(bbb, aaa, nnn, k2)
            call shmem_udcflush()
            ibar=barrier()

#endif
c     
c     add data received to local array
         
           do i=1,nnn
            
              aaa(i)=bbb(i)+aaa(i)
            
           enddo
            
         endif
         kk=2*kk
         
      enddo
#endif
#endif
      return
      end