to_string Function

pure function to_string(val, width) result(string)
   integer, intent(in) :: val
   integer, intent(in), optional :: width
   character(len=:), allocatable :: string
   integer, parameter :: buffer_len = range(val)+2
   character(len=buffer_len) :: buffer
   integer :: pos
   integer :: n
   character(len=1), parameter :: numbers(0:9) = &
      ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]

   if (val == 0) then
      if (present(width)) then
         string = repeat(" ", width-1) // numbers(0)
      else
         string = numbers(0)
      end if
      return
   end if

   n = abs(val)
   buffer = ""

   pos = buffer_len + 1
   do while (n > 0)
      pos = pos - 1
      buffer(pos:pos) = numbers(mod(n, 10))
      n = n/10
   end do
   if (val < 0) then
      pos = pos - 1
      buffer(pos:pos) = '-'
   end if

   if (present(width)) then
      string = repeat(" ", max(width-(buffer_len+1-pos), 0)) // buffer(pos:)
   else
      string = buffer(pos:)
   end if
end function to_string