def read_bignum
      sign = read_char == '-' ? -1 : 1
      size = read_fixnum * 2
      result = 0
      (0...size).each do |exp|
        result += read_char.ord * 2**(exp * 8)
      end
      result = result.to_i * sign
      @object_cache << result
      result
    end
def read_bignum
      sign = read_char == '-' ? -1 : 1
      size = read_fixnum * 2
      result = 0
      (0...size).each do |exp|
        result += read_char.ord * 2**(exp * 8)
      end
      result = result.to_i * sign
      @object_cache << result
      result
    end
Reads and returns Bignum from an input stream