subroutine masset (im1, im2)
c
c-----------------------------------------------------------------------
c routine to define a mass setting range
c-----------------------------------------------------------------------
c
      byte line(6), txt(4,6)
c
      integer masses(2,4), itab(2,6), im1, im2
c
      data txt/'H','+',2*0, 'H','E','+',0, 'H','E','+','+',
     *         'O','+',2*0, 'O','+','+',0, 'N','+',2*0/
      data itab/1, 0, 2, 1, 3, 0, 0, 2, 0, 3, 0, 4/
c
c-----------------------------------------------------------------------
c     *** get mass lookup table ***
c-----------------------------------------------------------------------
c
      call mastab (masses)
c
c-----------------------------------------------------------------------
c     *** prompt for the mass ***
c-----------------------------------------------------------------------
c
   25 write (*, 50)
   50 format(' Give species [e.g. L/H+] or <ret> to ',
     *         'enter settings: ', $)
      read (*, '(q, 9a1)') n, (line(i),i=1,n)
      if (n .eq. 0) go to 80
      if (n .lt. 4) go to 25
c
c-----------------------------------------------------------------------
c     *** determine if lo/hi mass channel ***
c-----------------------------------------------------------------------
c
      ilohi = 0
      if (line(1) .eq. 'l'  .or.  line(1) .eq. 'L') ilohi = 1
      if (line(1) .eq. 'h'  .or.  line(1) .eq. 'H') ilohi = 2
      if (ilohi. eq. 0) go to 25
      if (line(2) .ne. '/') go to 25
c
c-----------------------------------------------------------------------
c     *** find the mass settings ***
c-----------------------------------------------------------------------
c
      do 70 im = 1, 6
         do 75 j = 3, n
            if (txt(j-2, im) .ne. line(j)) go to 70
   75    continue
         ij = itab(ilohi, im)
         if (ij .eq. 0) go to 25
         jm1 = masses(1, ij)
         jm2 = masses(2, ij)
         if (ilohi .eq. 1) then
            jm1 = -4 * jm1
            jm2 = -4 * jm2
         end if
         go to 85
   70 continue
      go to 25
c
c-----------------------------------------------------------------------
c     *** enter mass settings explicitly ***
c-----------------------------------------------------------------------
c
   80 write (*, '('' give settings : '', $)')
      read (*,*) jm1, jm2
   85 continue
      im1 = min0(jm1, jm2)
      im2 = max0(jm1, jm2)
c
c-----------------------------------------------------------------------
c-----------------------------------------------------------------------
c
      return
      end