1. Rules
Assume that A and B are both positive numbers
addition:
Integer: [A]'s complement + [B]'s complement = [A+B]'s complement (mod 2^(n+1))
Decimal: [A]'s complement + [B]'s complement = [A+B]'s complement (mod 2)
Subtraction:
Integer: [AB]'s complement = [A]'s complement + [-B]'s complement (mod 2^(n+1))
Decimal: [AB]'s complement = [A]'s complement + [-B]'s complement (mod 2)
The method of finding the complement of [-B] is to add one to the negation of each bit, including the sign bit of the complement of [B].
Two, example
A = +15, B = +24, find [AB] complement
Convert to binary source code:
A = +15 = 0,0001111;
B = +24 = 0,0011000
Change to complement:
[A] Complement = 0,0001111,
[B] complement = 0,0011000,
[-B] complement=1,1101000
[AB] Complement = [A] Complement + [-B] Complement
0,0001111 +1,1101000
= 1,1110111