1/19/2008
Copyright
2005 – Tim Hoerning
20
2’s complement
•There are multiple methods of expressing negative numbers in binary.
–One of the more common is 2’s complement. This is the only one we will consider in this presentation
–Another method, sign magnitude, is common in digital
signal processors.
•Consider a k bit system
–Positive numbers 0—2(k-1) are simply their binary equivalent
–Negative numbers are -2k— -1are set to the binary number that will yield zero when added to the positive version. (ex, in a 3 bit system, 3 = 011,
then -3 would need to be 101 because
011 + 101 = 1000, but since it
is three bits, there is an overflow and that is really 000 or zero)