    # File lib/active_support/secure_random.rb, line 164
          def self.random_number(n=0)
            if 0 < n
              hex = n.to_s(16)
              hex = '0' + hex if (hex.length & 1) == 1
              bin = [hex].pack("H*")
              mask = bin[0]
              mask |= mask >> 1
              mask |= mask >> 2
              mask |= mask >> 4
              begin
                rnd = SecureRandom.random_bytes(bin.length)
                rnd[0] = rnd[0] & mask
              end until rnd < bin
              rnd.unpack("H*")[0].hex
            else
              # assumption: Float::MANT_DIG <= 64
              i64 = SecureRandom.random_bytes(8).unpack("Q")[0]
              Math.ldexp(i64 >> (64-Float::MANT_DIG), -Float::MANT_DIG)
            end
          end