# Returns the `base64` equivalent of `self`
	#
	# REQUIRE `self`.`is_base64_char`
	fun to_base64_char: Int do
		if self == u'+' then return 62
		if self == u'/' then return 63
		if self > u'Z' then
			if self < u'a' then abort
			if self <= u'z' then return self - 71
			abort
		end
		if self >= u'A' then return self - 0x41
		if self <= u'9' and self >= u'0' then return self + 4
		abort
	end