# A signed big-endian representation of `self`
	#
	# ~~~
	# assert     1.to_bytes.hexdigest ==     "01"
	# assert   255.to_bytes.hexdigest ==     "FF"
	# assert   256.to_bytes.hexdigest ==   "0100"
	# assert 65535.to_bytes.hexdigest ==   "FFFF"
	# assert 65536.to_bytes.hexdigest == "010000"
	# ~~~
	#
	# Negative values are converted to their two's complement.
	# Be careful as the result can be ambiguous.
	#
	# ~~~
	# assert     (-1).to_bytes.hexdigest ==     "FF"
	# assert    (-32).to_bytes.hexdigest ==     "E0"
	# assert   (-512).to_bytes.hexdigest ==   "FE00"
	# assert (-65794).to_bytes.hexdigest == "FEFEFE"
	# ~~~
	#
	# Optionally, set `n_bytes` to the desired number of bytes in the output.
	# This setting can disambiguate the result between positive and negative
	# integers. Be careful with this parameter as the result may overflow.
	#
	# ~~~
	# assert        1.to_bytes(2).hexdigest ==     "0001"
	# assert    65535.to_bytes(2).hexdigest ==     "FFFF"
	# assert     (-1).to_bytes(2).hexdigest ==     "FFFF"
	# assert   (-512).to_bytes(4).hexdigest == "FFFFFE00"
	# assert 0x123456.to_bytes(2).hexdigest ==     "3456"
	# ~~~
	#
	# For 0, a Bytes object with single nul byte is returned (instead of an empty Bytes object).
	#
	# ~~~
	# assert 0.to_bytes.hexdigest == "00"
	# ~~~
	#
	# For positive integers, `Bytes::to_i` can reverse the operation.
	#
	# ~~~
	# assert 1234.to_bytes.to_i == 1234
	# ~~~
	#
	# Require self >= 0
	fun to_bytes(n_bytes: nullable Int): Bytes do

		# If 0, force using at least one byte
		if self == 0 and n_bytes == null then n_bytes = 1

		# Compute the len (log256)
		var len = 1
		var max = 256
		var s = self.abs
		while s >= max do
			len += 1
			max *= 256
		end

		# Two's complement
		s = self
		if self < 0 then
			var ff = 0
			for j in [0..len[ do
				ff *= 0x100
				ff += 0xFF
			end

			s = ((-self) ^ ff) + 1
		end

		# Cut long values
		if n_bytes != null and len > n_bytes then len = n_bytes

		# Allocate the buffer
		var cap = n_bytes or else len
		var res = new Bytes.with_capacity(cap)

		var filler = if self < 0 then 0xFF else 0
		for i in [0..cap[ do res[i] = filler

		# Fill it starting with the end
		var i = cap
		var sum = s
		while i > cap - len do
			i -= 1
			res[i] = sum % 256
			sum /= 256
		end

		return res
	end