private fun substring_impl(from, count, end_index: Int): String do
		var cache = _position
		var dfrom = (cache - from).abs
		var dend = (end_index - from).abs

		var bytefrom: Int
		var byteto: Int
		if dfrom < dend then
			bytefrom = char_to_byte_index(from)
			byteto = char_to_byte_index(end_index)
		else
			byteto = char_to_byte_index(end_index)
			bytefrom = char_to_byte_index(from)
		end

		var its = _items
		byteto += its.length_of_char_at(byteto) - 1

		var s = new FlatString.full(its, byteto - bytefrom + 1, bytefrom, count)
		return s
	end