subroutine fslave ()      include 'p4f.h'*-----*  file:- norm_slave.f**  Test program for new p4 fortran library.*    Receive vector from master,*    compute sum norm,*    send result back to master.**  features:-*    max vector length <= 200   (controlled by `NMAX')*    4 data byte per integer    (controlled by `LENINT')*    4 data byte per item       (real; controlled by `LENREAL')**  Debug code disabled by `c$$$'.*  status:- plain vanilla, no error control*  Volker Kurz, ANL & U Frankfurt, 03-Oct-91*-----*     .. p4 routines ..      external   p4myid, p4recv, p4send**     .. constants ..      integer    NMAX,      LENINT,   LENREAL,   OFF,    MASTER      parameter (NMAX=200 , LENINT=4, LENREAL=4, OFF=-1, MASTER=0)      integer    TAGCNT,    TAGDAT,    TAGNEW,    TAGEND      parameter (TAGCNT=10, TAGDAT=20, TAGNEW=30, TAGEND=40)      real       ZERO      parameter (ZERO=0.0)**     .. variables and arrays ..      integer    myid, n, i, itype, iretcd, ireclen, iproc, msglen      real       v(NMAX), rnorm*-----      myid = p4myid()c$$$      write (*,*) 'slave ', myid, ' ready.'c$$$      call flush ()**  Outer loop for different matrices*  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1    continue**     .. receive vector length ..      itype = OFF      iproc = MASTER      call p4recv (itype, iproc, n, LENINT, ireclen, iretcd)c$$$      write (*,*) 'retcod from recv = ', iretcd, ' id = ', myidc$$$      write (*,*) 'ireclen from recv = ', ireclen, ' id = ', myidc$$$      call flush      if (itype.eq.TAGEND) then         write (*,*) 'slave', myid, ' ended normally'         return      elseif (itype.ne.TAGCNT) then         write (*,*)     $        'slave', myid, ' received unexpected data type:', itype         return      endif*  Main loop for calculation*  ~~~~~~~~~~~~~~~~~~~~~~~~~*  Receive one vector at a time from 'MASTER'.  *  Decide upon data type 'itype', whether norm shall be computed*  or program terminated.*  Watch out for unknown data type.* 2    continue*        .. receive vector ..         itype = OFF         iproc = MASTER         msglen = n*LENREALc$$$         write (*,*) 'recving vec  id = ', myidc$$$         call flush         call p4recv (itype, iproc, v, msglen, ireclen, iretcd)c$$$         write (*,*) 'recvd vec  id = ', myidc$$$         call flush         if (itype.eq.TAGDAT) then*           .. compute norm ..            rnorm = ZERO            do 22 i=1,n               rnorm = rnorm + abs (v(i)) 22         continue *           .. send result to host ..            call p4send (TAGDAT, MASTER, rnorm, LENREAL, iretcd)         elseif (itype.eq.TAGNEW) then*           .. end of outer loop for matrices ..            goto 1         elseif (itype.eq.TAGEND) then            write (*,*) 'slave', myid, ' ended normally'            return         else            write (*,*)     $           'slave', myid, ' received unexpected data type:', itype            return         endif      goto 2*-----      end