PROGRAM life
      IMPLICIT NONE

!
!     MAXLOOP iterations of an NxN life board
!
      INTEGER :: N, MAXLOOP
      INTEGER, ALLOCATABLE, DIMENSION(:,:,:) :: step
      INTEGER loop, i, j, cr, nx, r, c, nb, ls
      CHARACTER*(16) name
	  REAL(8) :: wall1, wall2, wall
!    
!     MPI variables
	  INTEGER :: my_rank=0, numprocs=1, ierr, tag
!  
	  INTEGER :: p, my_start, my_end, my_out_col0, my_out_col1, my_cols, loc_out_col0, loc_out_col1
	  INTEGER :: my_inn_col0, my_inn_col1, loc_inn_col0, loc_inn_col1, istart, iend
!
!     MPI initialization
!
!
!     Initialization
!
	  IF ( my_rank == 0 ) THEN
	  	  WRITE(*,*) " N, MaxLoop ?"
!	  	  READ*,N,MAXLOOP
	      N = 200; MAXLOOP = 32
	  	  ! Allocate full step board
	  	  ALLOCATE(step(N,N,2), STAT=ierr)
	  	  IF ( ierr /= 0 ) THEN
	  	  	  WRITE(*,*) " Error allocating step(N,N,2)"
	  	  	  ierr = -1
	  	  	  CALL Terminate(my_rank,ierr)
	  	  	  STOP
	  	  END IF
!         Initialize step
          step = 0
!         Ten active cells in a line
          step(N/2,((N/2)-5):((N/2)+4),1) = 1
!
!         Print starting config to file Life0000.pgm
!
	      loop = 0
	      WRITE(name,"(A4,I4.4)") "Life",loop
          CALL INTDATA2MPGM(N,N,step(:,:,1),name,4)
      END IF
      !  Send initial data to processes

      IF ( my_rank == 0 ) THEN
         CALL ProcessBand(N,my_start,my_end,numprocs,my_rank)    !  Global columns
	      my_out_col0 = MAX(my_start-1,1)   ! First allocated column in global numeration
          my_out_col1 = MIN(my_end+1,N)     ! Last allocated column in global numeration
          my_inn_col0 = my_out_col0 + 1
          my_inn_col1 = my_out_col1 - 1
          my_cols = (my_out_col1-my_out_col0+1) ! Total allocated columns

         !  Send process data

      ! ELSE   ! my_rank > 0  receive data

	  END IF

      loc_out_col0 = 1   ! First allocated column in local numeration
      loc_inn_col0 = 2   ! First column to be computed in local numeration
      loc_out_col1 = loc_out_col0 + my_out_col1 - my_out_col0
      loc_inn_col1 = loc_inn_col0 + my_inn_col1 - my_inn_col0   ! Last column to be computed in local numeration
!
!     Perform MAXLOOP updates
!  
      DO loop = 1, MAXLOOP
         cr = 2-mod(loop,2)
         nx = 2-mod(loop+1,2)
         ! Send border values
         IF ( my_end < N ) then   
 	  	       ! Send my rightmost column to left border of receiver
         END IF  
         IF ( my_start > 1 ) then   
 	  	      ! Send my leftmost column to right border of receiver
         END IF
         ! Acquire border values
         IF ( my_start > 1 ) then   
 	  	      ! Acquire left border
         END IF  
         IF ( my_end < N ) then   
 	  	      ! Acquire right border
         END IF
         DO r = 2, N-1
            DO c = loc_inn_col0, loc_inn_col1   ! local columns
               step(r,c,nx) = step(r,c,cr)   ! Inizialize cell
               !  Per each cell
               nb = 0
               DO i = r-1,r+1
                  DO j = c-1,c+1
                      ! Count active neighbours
                  	  IF ( .NOT. (i == r .AND. j == c) ) THEN
                  	  	  nb = nb + step(i,j,cr)
                  	  END IF
                  END DO
               END DO
               IF (nb.lt.2 .or. nb.gt.3) THEN
                  step(r,c,nx) = 0
               ELSE IF (nb.eq.3) THEN
                  step(r,c,nx) = 1
               END IF
            END DO
         END DO
!
!        Send data to root process
!        

	 ! IF ( my_rank == 0 ) THEN
	 	 ! receives data
	 ! ELSE   ! Send data to root 
	 ! END IF	    
         IF ( my_rank == 0 ) THEN
!
!           Write out computed state of board
!
       	    WRITE(name,"(A4,I4.4)") "Life",loop
            CALL INTDATA2MPGM(N,N,step(:,:,nx),name,4)
         END IF
      END DO

      ! processes should synchronize here
      ierr = 0
      CALL Terminate(my_rank,ierr)

   END PROGRAM life

      
subroutine IntData2Mpgm(s1,s2,idata,name,Mag)
!  Simple subroutine to dump integer data in a PGM format
   implicit none
   INTEGER, INTENT(IN) :: s1, s2, Mag
   INTEGER, DIMENSION(s1,s2), intent(in) :: idata
   character(*), intent(in) :: name
!
   integer :: i, j, ouni, r, m
   integer :: vp, vs
   real :: rmin, rmax
   character(80) :: fname
!
!  Write on unit 700 with  PGM format
   ouni = 700
   fname = TRIM(name)//".pgm"
   open(ouni,file=trim(fname),status="replace",iostat=vs)
   if ( vs /= 0 ) then
      WRITE(*,*) "!!!! Error write access to file ",trim(fname)
   end if
!  Magic code
   write(ouni,"(a)") "P2"
!  Dimensions
   write(ouni,*) s1*Mag, s2*Mag
!  Maximum value
   write(ouni,"(a)") "255"
!  Values from 0 to 255
   rmin = MINVAL(idata); rmax = MAXVAL(idata)
   vs = 0
   do i = 1, s1
      DO r = 1, Mag
      do j = 1, s2
         vp = INT ( (idata(i,j) - rmin) * 255.0 / (rmax - rmin) )
         DO m = 1, Mag
            write(ouni,"(i4)",advance="no") vp
            vs = vs + 1
         END DO
         if (vs >= 10 ) then
            write(ouni,"(a)") " "
            vs = 0
         end if
      end do
      write(ouni,"(a)") " "
      vs = 0
      END DO
   end do
   close(ouni)
   return
end subroutine IntData2Mpgm


SUBROUTINE ProcessBand(length,istart,iend,intervals,n)
      IMPLICIT NONE
      INTEGER, INTENT(IN) :: length,intervals,n
      INTEGER, INTENT(OUT) :: istart,iend
!
      INTEGER :: delta
!
      delta = ( length + (intervals - 1) ) / intervals
      istart = delta * n + 1; iend = delta * ( n + 1)
      if ( iend > length ) iend = length
!  
      RETURN
END SUBROUTINE ProcessBand
      

SUBROUTINE Terminate(p,rc)
    IMPLICIT NONE
!
    INTEGER, INTENT(IN) :: P
    INTEGER, INTENT(IN OUT) :: rc
    INTEGER :: ierr
 
    WRITE(*,*) "Process ",p," terminates"
 
    STOP
END SUBROUTINE Terminate