# `self` as a hexdigit to its byte value
	#
	# ~~~nit
	# intrude import core::bytes
	# assert 0x39.hexdigit_to_byteval == 0x09
	# assert 0x43.hexdigit_to_byteval == 0x0C
	# ~~~
	#
	# REQUIRE: `self.is_valid_hexdigit`
	private fun hexdigit_to_byteval: Int do
		if self >= 0x30 and self <= 0x39 then
			return self - 0x30
		else if self >= 0x41 and self <= 0x46 then
			return self - 0x37
		else if self >= 0x61 and self <= 0x66 then
			return self - 0x57
		end
		# Happens only if the requirement is not met.
		# i.e. this abort is here to please the compiler
		abort
	end