def _GetNormalizedTimestamp(self):
if self._normalized_timestamp is None:<EOL><INDENT>if (self._timestamp is not None and self._timestamp >= <NUM_LIT:0> and<EOL>self._timestamp <= self._UINT32_MAX):<EOL><INDENT>self._normalized_timestamp = (<EOL>decimal.Decimal(self._timestamp) - self._HFS_TO_POSIX_BASE)<EOL><DEDENT><DEDENT>return self._normalized_timestamp<EOL>
Retrieves the normalized timestamp.

        Returns:
          decimal.Decimal: normalized timestamp, which contains the number of
              seconds since January 1, 1970 00:00:00 and a fraction of second used
              for increased precision, or None if the normalized timestamp cannot be
              determined.