# Returns a new `Bytes` instance with the digest as content
	#
	#     assert "0B1F4D".hexdigest_to_bytes == [0x0B, 0x1F, 0x4D]
	#     assert "0B1F4D".hexdigest_to_bytes.hexdigest == "0B1F4D"
	#
	# Characters that are not hexadecimal digits are ignored.
	#
	#     assert "z0B1 F4\nD".hexdigest_to_bytes.hexdigest == "0B1F4D"
	#     assert "\\x0b1 \\xf4d".hexdigest_to_bytes.hexdigest == "0B1F4D"
	#
	# When the number of hexadecimal digit is not even, then a leading 0 is
	# implicitly considered to fill the left byte (the most significant one).
	#
	#     assert "1".hexdigest_to_bytes.hexdigest == "01"
	#     assert "FFF".hexdigest_to_bytes.hexdigest == "0FFF"
	#
	# `Bytes::hexdigest` is a loosely reverse method since its
	# results contain only pairs of uppercase hexadecimal digits.
	#
	#     assert "ABCD".hexdigest_to_bytes.hexdigest == "ABCD"
	#     assert "a b c".hexdigest_to_bytes.hexdigest == "0ABC"
	fun hexdigest_to_bytes: Bytes do
		var b = bytes
		var max = byte_length

		var dlength = 0 # Number of hex digits
		var pos = 0
		while pos < max do
			var c = b[pos]
			if c.is_valid_hexdigit then dlength += 1
			pos += 1
		end

		# Allocate the result buffer
		var ret = new Bytes.with_capacity((dlength+1) / 2)

		var i = (dlength+1) % 2 # current hex digit (1=high, 0=low)
		var byte = 0 # current accumulated byte value

		pos = 0
		while pos < max do
			var c = b[pos]
			if c.is_valid_hexdigit then
				byte = byte << 4 | c.hexdigit_to_byteval
				i -= 1
				if i < 0 then
					# Last digit known: store and restart
					ret.add byte
					i = 1
					byte = 0
				end
			end
			pos += 1
		end
		return ret
	end