subroutine getcts(modblk,cts,ctn,i1,i2,jflag)
c
c this subroutine gets data for a given head and given mass.
c cts and ctn are updated with all the samples i1 thru i2, that satisfy
c the modblk requirements.
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 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 13 aug 82
c v1.1 jfej        17 aug 82 added idcodc call
c v1.2 rlwest       8 jul 86 incorporated new version if idcodc
c
      integer*2 idat(2812),icde(512,2),jcr(512,2)
      integer*4 idcodc, ictn
      integer*4 jrpa(512),jmsh(512),modblk(8)
      equivalence (icde(1,1),idat(1789))
      equivalence (jcr(1,1),idat(253))
      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.1)go to 401
c             z head processing
      idet=(modblk(1)-2)*2+modblk(2)
c      call getzms(idet,izms)
      do 430 i=i1,i2
c             check that rpa setting is in the required range
      if(jrpa(i).lt.modblk(5).or.jrpa(i).gt.modblk(6))go to 430
c             check that this mass is in the range required
      if(jmsh(i).lt.modblk(3).or.jmsh(i).gt.modblk(4))go to 430
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 430
c             check we have data for this z head detector
      izms=igtzms(idet,i)
      if(izms.le.0)go to 430
      jflag=1
      cts=cts+float(idcodc(icde(i,izms),ictn))
      ctn=ctn+ictn
  430 continue
  410 continue
      go to 400
c
  401 continue
c             radial head processing
      do 100 i=i1,i2
c             check that rpa setting is in the required range
         if(jrpa(i).lt.modblk(5).or.jrpa(i).gt.modblk(6))go to 100
c             check that this mass is in the range required
         if(jmsh(i).lt.modblk(3).or.jmsh(i).gt.modblk(4))go to 100
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 100
         jflag=1
         cts=cts+float(idcodc(jcr(i,modblk(2)),ictn))
         ctn=ctn+ictn
  100 continue
c
  400 continue
      return
      end