**The Free On-line Dictionary of Computing (30 December 2018):**

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)