code: func (otp *HOTP) Check(code string) bool {
  	codeBytes := []byte(code)
  	genCode := []byte(otp.OTP())
  	if subtle.ConstantTimeCompare(codeBytes, genCode) != 1 {
  		otp.setCounter(otp.Counter() - 1)
  		return false
  	}
  	return true
  }
docs: // Check takes an input code and verifies it against the OTP. If
  // successful, the counter is incremented.