ALU 101 Overflow and Error Handling

Question 1

What is integer overflow in the context of ALU operations?

Accepted Answer

When an arithmetic result exceeds the maximum value that can be stored in the destination register

Answer

Integer overflow occurs when a computation produces a value larger (or smaller, for negative) than the register's representable range, causing an incorrect result.

Question 2

In two's complement addition, how can you detect signed overflow using the carry-in and carry-out of the MSB?

Accepted Answer

Overflow = carry-in XOR carry-out of the MSB

Answer

Signed overflow is detected when the carry into the sign bit differs from the carry out of the sign bit, an XOR of those two carry values.

Question 3

What distinguishes unsigned overflow (carry) from signed overflow in ALU results?

Accepted Answer

Unsigned overflow (CF) means the result exceeded the unsigned range; signed overflow (OF) means it exceeded the two's complement range

Answer

CF and OF are separate flags: CF indicates the result doesn't fit in the unsigned range, while OF indicates it doesn't fit in the signed range for the same bit width.

Question 4

What happens in most hardware ALUs when integer overflow is not handled explicitly?

Accepted Answer

The result wraps around modulo 2^n, potentially producing an incorrect silent error

Answer

Without overflow trapping, the ALU simply truncates the result to n bits, wrapping around, and the overflow flag is set but often ignored by software.

Question 5

Which programming practice helps prevent integer overflow errors when using ALU results in software?

Accepted Answer

Checking operand ranges before the operation or using overflow-checking arithmetic libraries

Answer

Pre-validating that operands won't cause overflow, or using language-level overflow-checked arithmetic, prevents silent data corruption.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 Overflow and Error Handling