Can negating a non-negative signed integer value ever overflow?

[Alex Fraser]

Can negating a non-negative signed integer value ever overflow? Put another
way, can it be true that (mathematically) INT_MIN > -INT_MAX, LONG_MIN

-LONG_MAX etc?

I know that typically it can't overflow, but if that isn't guaranteed, how
can I portably detect if it would?

Alex

 

[Jordan Abel]

Can negating a non-negative signed integer value ever overflow? Put another
way, can it be true that (mathematically) INT_MIN > -INT_MAX, LONG_MIN

I know that typically it can't overflow, but if that isn't guaranteed, how
can I portably detect if it would?

Alex

C99 only allows twos-complement, ones-complement, and signed-magnitude
representation. It is unclear what C89 allows.

 

[pete]

Can negating a non-negative signed integer value ever overflow?

No.

 

[Alex Fraser]

C99 only allows twos-complement, ones-complement, and signed-magnitude
representation.

Which implies INT_MIN is either -INT_MAX (one's complement or sign and
magnitude) or -INT_MAX - 1 (two's complement), etc, so that's OK.

It is unclear what C89 allows.

Hmm. A shame.

I know it normally can't overflow, and I can't see how to detect if it
could/would overflow anyway, so I guess should shrug my shoulders and move
on .

Thanks,
Alex

 

[Joe Wright]

No.

No context? Chuck is gonna getcha.

Assume 2's complement.

int i = INT_MIN;

This is -2147483648 and 0x80000000. If then..

i = -i;

...the result is the same. Did anything happen? Was it overflow?

 

[Richard Heathfield]

Joe Wright said:

No context? Chuck is gonna getcha.

Assume 2's complement.

int i = INT_MIN;

This is -2147483648 and 0x80000000. If then..

i = -i;

..the result is the same. Did anything happen? Was it overflow?

This may have escaped your notice, I know - but -2147483648 does not quite
qualify as non-negative, so it falls outside the domain of the question.

 

[Keith Thompson]

No context? Chuck is gonna getcha.

What do you mean? pete quoted the relevant portion of the parent
article, including the attribution line, and answered the question.
(And Richard already pointed out your other error.)

 

[CBFalconer]

What do you mean? pete quoted the relevant portion of the parent
article, including the attribution line, and answered the question.
(And Richard already pointed out your other error.)

Yes, I saw no reason to unleash the slavering dogs.

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[Joe Wright]

Yes, I saw no reason to unleash the slavering dogs.

Sorry pete. Thanks Richard, Keith and Chuck for catching me up. I read
pete's one liner as..
"Can negating a negative signed integer value ever overflow?"