The ALU supported set on less than (slt) using just the sign bit of the adder. Let’s try a set on less than operation using the values -7_ten and 6_ten.
To make it simpler to follow the example, let’s limit the binary representations to 4 bits: 1001_two and 0110_two.

1001_two – 0110_two = 1001_two + 1010_two = 0011_two

This result would suggest that -7 > 6, which is clearly wrong. Hence, we must factor in overflow in the decision. Modify the 1-bit ALU in Figure B.5.10 on page B-33 to handle slt correctly. Make your changes on a photocopy of this figure to save time.