extract_same_part_suffix Function

   pure function extract_same_part_suffix (a, b) result(res)
      use :: forgex_utf8_m
      implicit none
      character(*), intent(in) :: a, b
      character(:), allocatable :: res
      
      character(:), allocatable :: buf
      integer :: i, ii, n, diff, ie
      character(:), allocatable :: short_s, long_s
      
      res = ''
      buf = ''

      if (len(a) < len(b)) then
         short_s = a 
         long_s = b
      else
         short_s = b
         long_s = a
      end if
 
      n = min(len(a), len(b))
      diff = max(len(a), len(b)) - n

      do i = n, 1, -1
         ii = i + diff
         if (short_s(i:i) == long_s(ii:ii)) then
            buf = a(i:i)//buf
         else
            exit
         end if
      end do

      n = len(buf)
      i= 1
      do while (i <= n)
         ie = idxutf8(buf, i)
         if (n < ie) exit
         
         if (is_valid_multiple_byte_character(buf(i:ie))) then
            res = res//adjustl_multi_byte(buf(i:ie))
         end if
         i = ie + 1
      end do
   end function extract_same_part_suffix