code: function branch( flag ) {
  		var offset = read(),
  			prevHigh = PC & HIGH,
  			curHigh = 0;
  
  		if ( flag ) {
  			// branching burns a cycle
  			burn(1);
  
  			if ( offset & 0x80 ) {
  				offset = -complement( offset );
  			}
  
  			PC += offset;
  			curHigh = PC & HIGH;
  
  			if ( prevHigh !== curHigh ) {
  				// crossing page boundary, burns a cycle
  				burn(1);
  			}
  		}
  	}
docs: Helper function for all branching operations.
  @param {boolean} flag - If true, do branch. Otherwise do nothing.