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When a program does arithmetic, it often has to make decisions based on the
results: whether overflow occurred, if the result is 0 or negative, if the
result is positive, and so forth. Thus, most computers have four bits
coming out of the adder which give this kind of information. These are:
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Carry bit
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C
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if there was a final carry out, this bit is 1.
This signals overflow if the two operands are unsigned.
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Negative bit
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N
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if the result of the addition is negative assuming 2's
complement, this bit is 1.
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Overflow bit
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V
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if there was an overflow after adding two 2's complement
numbers, this bit is 1.
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Zero bit
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Z
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if the result of the addition is 0 (all 0s),
this bit is 1.
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