private long diode(long offset, long length) {
		int lb = (int) (64 - offset);
		int rb = (int) (64 - (offset + length));
		return (-1L << lb) ^ (-1L << rb);
	}
private long diode ( long offset , long length ) { int lb = ( int ) ( 64 - offset ) ; int rb = ( int ) ( 64 - ( offset + length ) ) ; return ( - 1L << lb ) ^ ( - 1L << rb ) ; }
a diode is a long value whose left and right margin are ZERO, while middle
bits are ONE in binary string layout. it looks like a diode in shape.

@param offset
left margin position
@param length
offset+length is right margin position
@return a long value