# File lib/multi_json/vendor/ok_json.rb, line 376
  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