subroutine srtrpa(modblk,cts,ictn,i1,i2,jflag)
c
c this subroutine sorts data for a given head and given mass in
c terms of instrument rpa setting.
c
c input arguments are:
c      modblk      see sentgs input subroutine
c      i1    - start sample index of data to be included
c      i2    - stop sample index. i1, i2 are in range [1,512]
c output arguments, in addition to cts, ctn,
c      jflag - set to 0 if no data added to arrays, otherwise 1
c
c the arrays cts(nang) and ictn(nang) are updated appropriately
c note *** before this routine is called, the information in the
c following common blocks must be defined
c      common      updated by calling
c      ------      ------------------
c      rpamsh      getmod.  contains instrument rpa, ims settings
c      i7flgs      deffgs.  contains instrument mode flags.
c
c v1.0 jfe johnson 25 jul 82
c v1.1 jfej        17 aug 82 added idcodc call
c v1.2 jl green         14 sept 82 added electrometer code
c
      integer*2 idat(2812),icde(512,2),jcr(512,2)
      integer*2 kcel(512)
      integer*4 idcodc, ic
      integer*4 jrpa(512),jmsh(512),modblk(8)
      integer*4 ictn(32)
      real cts(32)
      equivalence (icde(1,1),idat(1789))
      equivalence (jcr(1,1),idat(253))
      equivalence (kcel(1),idat(1277))
      common/rpamsh/jrpa,jmsh
      common/maf1/idat
c
      jflag=0
c
c first call refang, to define phase angle reference
c
      call refang(degsam,ramang)
c
      if(modblk(1).eq.4)go to 1000
      if(modblk(1).eq.1)go to 601
c z head processing
      idet=(modblk(1)-2)*2+modblk(2)
      do 630 i=i1,i2
      irp=isclrp(jrpa(i))
      if(irp.lt.1)go to 630
c check this sample is in the angle range required
      iang=isangl(degsam,ramang,i)
      if(iang.lt.modblk(7).or.iang.gt.modblk(8))go to 630
c check that this mass is in the range required
      if(jmsh(i).lt.modblk(3).or.jmsh(i).gt.modblk(4))go to 630
c check we have data for this z head detector
      ich=igtzms(idet,i)
      if(ich.le.0)go to 630
      jflag=1
      cts(irp)=cts(irp)+idcodc(icde(i,ich),ic)
      ictn(irp)=ictn(irp)+ic
  630 continue
  610 continue
      go to 9000
c
  601 continue
c radial head processing
      do 700 i=i1,i2
      irp=isclrp(jrpa(i))
      if(irp.lt.1)go to 700
c check this sample is in the angle range required
      iang=isangl(degsam,ramang,i)
      if(iang.lt.modblk(7).or.iang.gt.modblk(8))go to 700
c check that this mass is in the range required
      if(jmsh(i).lt.modblk(3).or.jmsh(i).gt.modblk(4))go to 700
      jflag=1
      cts(irp)=cts(irp)+idcodc(jcr(i,modblk(2)),ic)
      ictn(irp)=ictn(irp)+ic
  700 continue
      go to 9000
c
c the electrometer channel
c
 1000 continue
      do 2000 i=i1,i2
      irp=isclrp(jrpa(i))
      if(irp.lt.1) go to 2000
c checking for angle range
      iang=isangl(degsam,ramang,i)
      if(iang.lt.modblk(7).or.iang.gt.modblk(8)) go to 2000
      jflag=1
      cts(irp)=cts(irp)+idcodc(kcel(i),ic)
      ictn(irp)=ictn(irp)+ic
 2000 continue
c
 9000 continue
      return
      end