redef fun substring(from, count) do
		if from < 0 then
			count += from
			if count < 0 then return ""
			from = 0
		end

		var ln = _length
		if (count + from) > ln then count = ln - from
		if count <= 0 then return ""
		var end_index = from + count - 1

		var flps = _flat_last_pos_start
		if from >= flps then
			var fc = _flat_cache
			if end_index < flps + fc._length then
				return fc.substring_impl(from - flps, count, end_index - flps)
			end
		end

		var lft = _left
		var llen = lft.length
		if from < llen then
			if from + count < llen then return lft.substring(from, count)
			var lsublen = llen - from
			return lft.substring_from(from) + _right.substring(0, count - lsublen)
		else
			return _right.substring(from - llen, count)
		end
	end

	redef fun substring(from, count)
	do
		if count <= 0 then return ""

		if from < 0 then
			count += from
			if count <= 0 then return ""
			from = 0
		end

		var ln = _length
		if (count + from) > ln then count = ln - from
		if count <= 0 then return ""
		var end_index = from + count - 1
		return substring_impl(from, count, end_index)
	end

	redef fun substring(from, count)
	do
		assert count >= 0
		if from < 0 then from = 0
		if (from + count) > _length then count = _length - from
		if count <= 0 then return new Buffer
		var its = _items
		var bytefrom = its.char_to_byte_index(from)
		var byteto = its.char_to_byte_index(count + from - 1)
		byteto += its.char_at(byteto).u8char_len - 1
		var byte_length = byteto - bytefrom + 1
		var r_items = new CString(byte_length)
		its.copy_to(r_items, byte_length, bytefrom, 0)
		return new FlatBuffer.with_infos(r_items, byte_length, byte_length, count)
	end

	redef fun substring(from, count) do
		var ln = _length
		if count <= 0 then return ""
		if (count + from) > ln then count = ln - from
		if count <= 0 then return ""
		if from < 0 then
			count += from
			if count <= 0 then return ""
			from = 0
		end
		return new ASCIIFlatString.full_data(_items, count, from + _first_byte, count)
	end