code: protected function readInt31( $pos = 0 ) {
  		$uint31 = $this->readInt32( $pos );
  		if ( $uint31 > 0x7fffffff ) {
  			throw new Exception(
  				'Error in CDB file "' . $this->fileName . '", integer too big.' );
  		}
  
  		return $uint31;
  	}
docs: Unpack an unsigned integer and throw an exception if it needs more than 31 bits.
  
  @param int $pos Position to read from.
  @throws Exception When the integer cannot be represented in 31 bits.
  @return int