Radix Complement Arithmetic (5)
Case 3: A = -B - C
- A = [B]2 + [C]2 = 2n - (B)2 + 2n - (C)2 = 2n + 2n - (B + C)2 = 2n + [B + C]2
- The carry bit (2n) is discarded.
- An overflow can occur, in which case the sign bit is 0.
- Example: -(7)10 - (8)10 = ?
- Perform (-(7)10) + (-(8)10)
- -(7)10 = -(0111)2 = (1, 1001)2cns , -(8)10 = -(1000)2 = (1, 1000)2cns
- -(7)10 - (8)10 = (1, 1001)2cns + (1, 1000)2cns = (1, 0001)2cns + carry
- Example: -(12)10 - (5)10 = ?
- Perform (-(12)10) + (-(5)10)
- -(12)10 = -(1100)2 = (1, 0100)2cns , -(5)10 = -(0101)2 = (1, 1011)2cns
- -(7)10 - (8)10 = (1, 0100)2cns + (1, 1011)2cns = (0, 1111)2cns + carry
- Overflow, because the sign bit is 0.