[issue1621] Do not assume signed integer overflow behavior

["Martin v. Löwis" <report@bugs.python.org> at psf.upfronthosting.co.za]

Martin v. Löwis <martin at v.loewis.de> added the comment:

> 	size = Py_SIZE(a) * n;
> 
> The multiplication should be safe from overflow, and I don't get
> any warning at all either with this rewrite (using -O3 -Wall -Wextra -
> Wsigned-overflow=5) or from the original code, so there's nothing to 
> silence.

This is puzzling, isn't it? It *could* overflow, could it not?

>> I think there is a second solution: perform the multiplication
>> unsigned in the first place.
> 
> That would work too.  I find the above code clearer, though.

I agree in this case. In general, I'm not convinced that it
is always possible to rewrite the code in that way conveniently.

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<http://bugs.python.org/issue1621>
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