资料来源 : Free On-Line Dictionary of Computing

twos complement
     
         A system used in some computers to represent negative
        numbers in {binary}.  Each {bit} of the number is inverted
        (zeros are replaced with ones and vice versa), as for {ones
        complement}, but then one (000...0001) is added (ignoring
        overflow).  This avoids the two representations for zero found
        in ones complement by using all ones to represent -1.
     
        	...
        	000...00011 = +3
        	000...00010 = +2
        	000...00001 = +1
        	000...00000 =  0
        	111...11111 = -1
        	111...11110 = -2
        	111...11101 = -3
        	...
     
        This representation simplifies the logic required for addition
        and subtraction, at the expense of a little extra complexity
        for negation.
     
        (1994-10-31)