# Encodes `self` to base64.
	#
	# By default, uses "=" for padding.
	#
	#     assert "string".encode_base64 == "c3RyaW5n"
	private fun encode_base64(length: Int): Bytes do
		var base64_bytes = once base64_chars
		var steps = length / 3
		var bytes_in_last_step = length % 3
		var result_length = steps * 4
		if bytes_in_last_step > 0 then result_length += 4
		var result = new Bytes.with_capacity(result_length)

		var in_off = 0
		for s in [0 .. steps[ do
			var ind = (self[in_off] & 0b1111_1100) >> 2
			result.add base64_bytes[ind]
			ind = ((self[in_off] & 0b0000_0011) << 4) | ((self[in_off + 1] & 0b1111_0000) >> 4)
			result.add base64_bytes[ind]
			ind = ((self[in_off + 1] & 0b0000_1111) << 2) | ((self[in_off + 2] & 0b1100_0000) >> 6)
			result.add base64_bytes[ind]
			ind = (self[in_off + 2] & 0b0011_1111)
			result.add base64_bytes[ind]
			in_off += 3
		end
		if bytes_in_last_step == 1 then
			result.add base64_bytes[(self[in_off] & 0b1111_1100) >> 2]
			result.add base64_bytes[(self[in_off] & 0b0000_0011) << 4]
		else if bytes_in_last_step == 2 then
			result.add base64_bytes[(self[in_off] & 0b1111_1100) >> 2]
			result.add base64_bytes[((self[in_off] & 0b0000_0011) << 4) | ((self[in_off + 1] & 0b1111_0000) >> 4)]
			result.add base64_bytes[(self[in_off + 1] & 0b0000_1111) << 2]
		end
		var rempad = if bytes_in_last_step > 0 then 3 - bytes_in_last_step else 0
		for i in [0 .. rempad[ do result.add u'='

		return result
	end