subroutine strtok(str_in,str_o1,str_o2,FS)
c
c split a character string str_in at the first occurrance of 
c the field separator FS into the first token str_o1 and a remainder 
c str_o2
c originally written by Fortunat Kind, modified by a.tento
c
        character str_in*(*), str_o1*(*), str_o2*(*)
        character*1 FS
c
        integer sep_index, beg_index, stop_index, m, i, jj
c
c
        m = len(str_in)
        do 1 i = 1, m
        beg_index = i
        if ( str_in(i:i)  .ne.  ' ' )  goto 2
1       continue
        goto 10
2       continue
c
        do 3 i = beg_index+1, m
        sep_index = i
        if ( str_in(i:i)  .eq.  FS ) goto 4
3       continue
        goto 10
4       continue
c
        jj = m - sep_index
        do 5 i = 1, jj
        stop_index = m + 1  - i
        if ( str_in(stop_index:stop_index)  .ne.  ' ' ) goto 6
5       continue
6       continue
c
        str_o1=str_in(beg_index:sep_index-1)
        str_o2=str_in(sep_index+1:stop_index)
c
        return
c
c
10      str_o1=str_in
        str_o2=''
c
        return
c
c
        end