Why overflow didn't happen in here

StackOverflow https://stackoverflow.com/questions/20143441

  •  03-08-2022
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Question

In my past paper answer sheet there is an answer given below:

123 = 01111011
-65 = 10111111
sum = 00111010
Carry occurs, but can be ignored. No overflow, the sum is correct sign.

What is the meaning of "the sum is correct sign?" Please explain.

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Solution

Sum is correct sign means that the msbit (in the 128's column) being 0 properly represents that the sum is positive.

No overflow means that the sum of 00111010 (58 decimal) can be represented in 8 bits.

Carry occurs, but can be ignored refers to the fact that the carry-in to the msbit occurs and matches the carry-out from the msbit, resulting in no overflow (and so can be ignored). When the carry-in to the msbit does not match the carry-out from the msbit, there is signed overflow.

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