Hello,

Here is an example:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46850

There was a long discussion surrounding this on the ITK dev list as well entitled "vxl update".

Brad

On Aug 1, 2011, at 1:10 PM, Stefan Atev wrote:

I would love to see an architecture on which vxl works and signed
overflow acts in a "undefined" way. Practically anything that needs
modulo 2^N arithmetic uses this...

Just because the compiler is technically free to anything it wants,
does not mean it won't do exactly what you want it to do, or that it
will go out of its way to subvert the underlying architecture. Show me
a processor family on which signed overflow is undefined and I'll show
you a dead architecture :)


Cheers,

Stefan


On Mon, Aug 1, 2011 at 8:54 AM, Markus Moll
<markus.moll@esat.kuleuven.be> wrote:
Hi

On Monday 01 August 2011 15:43:15 Sean McBride wrote:
Peter,

Thanks for your reply.

The thing is, signed overflow is undefined, meaning the compiler is free to
do whatever it wants, because a correct program must never overflow.

What's worse: at least one popular compiler (gcc) is kind of infamous for
aggressively exploiting that freedom, even in completely non-obvious
circumstances.

Markus


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Bradley Lowekamp  

Lockheed Martin Contractor for

Office of High Performance Computing and Communications

National Library of Medicine 

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