def _GetNormalizedTimestamp(self):
if self._normalized_timestamp is None:<EOL><INDENT>if (self._timestamp is not None and self._timestamp >= self._INT64_MIN and<EOL>self._timestamp <= self._INT64_MAX):<EOL><INDENT>self._normalized_timestamp = (<EOL>decimal.Decimal(self._timestamp) /<EOL>definitions.MICROSECONDS_PER_SECOND)<EOL>self._normalized_timestamp -= self._WEBKIT_TO_POSIX_BASE<EOL><DEDENT><DEDENT>return self._normalized_timestamp<EOL>
Retrieves the normalized timestamp.

        Returns:
          float: 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.