subroutine mastxt (im1, im2, ilohi, txtlm, txthm)
c
c-----------------------------------------------------------------------
c Routine returns text strings corresponding to the mass species
c which are detected in low mass det (txtlm) and high mass
c detector (txthm) with mass setting range of im1 to im2.
c
c if either of im1, im2 is outside the defined range
c both txtlm and txthm are set to '????'.
c
c *NOTE* ORDER OF ELEMENTS IN MASS ARRAY MUST MATCH TEXT IN TXTL/TXTH
c-----------------------------------------------------------------------
c
      byte quest, txth(4,4), txthm(4), txtl(4,4), txtlm(4)
c
      integer mass(2,4)
c
      data quest/'?'/
      data txtl/'H','+',' ',' ',  'H','E','+',' ',  'H','E','+','+',
     *          '3','.','5',' '/
      data txth/'H','E','+',' ',  'O','+',' ',' ',  'O','+','+',' ',
     *          'N','+',' ',' '/
c
c-----------------------------------------------------------------------
c-----------------------------------------------------------------------
c
      call mastab (mass)
c
c-----------------------------------------------------------------------
c     *** determine lo/hi channel and mass settings ***
c-----------------------------------------------------------------------
c
      ilohi = 2
      if (im1 .lt. 0  .and.  im2 .lt. 0) ilohi = 1
      jm1 = im1
      jm2 = im2
      if (ilohi .eq. 1) then
         jm1 = -jm1 / 4
         jm2 = -jm2 / 4
      end if
      jm1 = min0(jm1, jm2)
      jm2 = max0(jm1, jm2)
      do im = 1, 4
         if(jm1 .ge. mass(1,im)  .and.  jm2 .le. mass(2,im)) go to 50
      end do
c
c-----------------------------------------------------------------------
c     *** undefined mass settings, so put in ???? ***
c-----------------------------------------------------------------------
c
      do i = 1, 4
         txtlm(i) = quest
         txthm(i) = quest
      end do
      return
c
c-----------------------------------------------------------------------
c     *** mass settings defined, so put in text ***
c-----------------------------------------------------------------------
c
   50 continue
      do i = 1, 4
         txtlm(i) = txtl(i,im)
         txthm(i) = txth(i,im)
      end do
c
c-----------------------------------------------------------------------
c-----------------------------------------------------------------------
c
      return
      end