subroutine srtang (modblk, cts, ctss, ictn, nang, is, ie, jflag)
c
c----------------------------------------------------------------------
c
c     This subroutine sorts data for a given head and given mass in
c     terms of instrument spin phase angle.
c
c----------------------------------------------------------------------
c
c input arguments are:
c
c      modblk     processing limits and parameters
c      nang       number of angle bins for one spin
c      is         start sample index of data to be included
c      ie         stop sample index. is, ie are in range [1,512]
c
c----------------------------------------------------------------------
c
c output arguments are:
c
c      cts        accumulated counts
c      ctss       accumulated counts**2
c      ictn       accumulates number of samples
c      jflag      set to 0 if no data added to arrays, otherwise 1
c
c the arrays cts(nang), ctss(nang)  and ictn(nang) are updated appropriately
c
c----------------------------------------------------------------------
c
c following common blocks must be defined
c
c      common      updated by calling
c      ------      ------------------
c      rpamsh      getmd1.  contains instrument rpa, ims settings
c      i7flgs      deffgs.  contains instrument mode flags.
c
c----------------------------------------------------------------------
c
      integer*2 icde(512,2), idat(2812), jcr(512,2), kcel(512)
c
      integer*4 i, iang, iangln, ic, ictn(nang), idcodc, ie, is, jflag,
     *          jmsh(512), jrpa(512), modblk(8), nang
c
      real      cts(nang), ctss(nang)
c
      common    /maf1/idat,
     *          /rpamsh/jrpa, jmsh
c
      equivalence (icde(1,1), idat(1789)),
     *            (jcr(1,1), idat(253)),
     *            (kcel(1), idat(1277))
c
c----------------------------------------------------------------------
c     *** set the have data flag ***
c----------------------------------------------------------------------
c
      jflag = 0
c
c----------------------------------------------------------------------
c     *** first call refang, to define phase angle reference ***
c----------------------------------------------------------------------
c
      call refang (degsam, ramang)
c
c----------------------------------------------------------------------
c     *** collect the data ***
c----------------------------------------------------------------------
c
      if (modblk(1) .eq. 1) then
c
c----------------------------------------------------------------------
c        *** radial head processing ***
c----------------------------------------------------------------------
c
c-----------------------------------------------------------------------
c        *** loop through the samples to process ***
c-----------------------------------------------------------------------
c
         do 100 i = is, ie
c
c----------------------------------------------------------------------
c           *** check that rpa setting is in the required range ***
c----------------------------------------------------------------------
c
            if(jrpa(i).lt.modblk(5) .or. jrpa(i).gt.modblk(6))go to 100
c
c----------------------------------------------------------------------
c           *** check that this mass is in the range required ***
c----------------------------------------------------------------------
c

            if(jmsh(i).lt.modblk(3) .or. jmsh(i).gt.modblk(4))go to 100
c
c----------------------------------------------------------------------
c           *** save the data ***
c----------------------------------------------------------------------
c
            jflag = 1
            iang = iangln(degsam, ramang, nang, i)
            cnt = idcodc(jcr(i,modblk(2)), ic)
            cts(iang) = cts(iang) + cnt
            ctss(iang) = ctss(iang) + cnt**2
            ictn(iang) = ictn(iang) + ic
  100    continue
c
c----------------------------------------------------------------------
c        *** end radial head processing ***
c----------------------------------------------------------------------
c
      else
      end if
c
c----------------------------------------------------------------------
c----------------------------------------------------------------------
c
      return
      end