# Returns self as an hexadecimal digest.
	#
	# Also known as plain hexdump or postscript hexdump.
	#
	# ~~~
	# var b = "abcd".to_bytes
	# assert b.hexdigest == "61626364"
	# assert b.hexdigest.hexdigest_to_bytes == b
	# ~~~
	fun hexdigest: String do
		var elen = length * 2
		var ns = new CString(elen)
		var i = 0
		var oi = 0
		while i < length do
			self[i].add_digest_at(ns, oi)
			i += 1
			oi += 2
		end
		return new FlatString.full(ns, elen, 0, elen)
	end