# File lib/rhc/vendor/okjson.rb, line 386
      def nibble(c)
        case true
        when ?0 <= c && c <= ?9 then c.ord - ?0.ord
        when ?a <= c && c <= ?z then c.ord - ?a.ord + 10
        when ?A <= c && c <= ?Z then c.ord - ?A.ord + 10
        else
          raise Error, "invalid hex code #{c}"
        end
      end