A little story

[bearophile]

Don Clugston:

> Bearophile, haven't you ever read that paper on integer 
> overflow, which you keep posting to the newsgroup???

I have read it time ago, but it seems not having run-time 
overflow tests is not an option for certain programming endeavors 
of mine. This is why I have partially switched back to FreePascal 
for those.


> It clearly demonstrates that it is NOT POSSIBLE to implement 
> integer overflow checking in a C-family language.

Clarke says something nice:
>When a distinguished but elderly scientist states that something 
>is possible, he is almost certainly right. When he states that 
>something is impossible, he is very probably wrong.<

http://embed.cs.utah.edu/ioc/


> Valid, correct, code which depends on integer overflow is very, 
> very common (when overflow occurs, it's more likely to be 
> correct, than incorrect).

I was discussing about an annotation to disable it locally where 
the programmer wants such overflows (like using wrap-around 
semantics to avoid testing for negative values. I have done this 
myself some times).

I am not interested in taking a quite optimized 80_000 lines long 
C program and switching on the run-time integral overflow tests 
on it all, all at once. This is probably going to fail, as the 
paper says. Smaller D programs written from zero with run-time 
overflow tests are one example of what I was thinking about.


> I don't think you could do it without introducing a no-overflow 
> integer type. The compiler just doesn't have enough information.

This solution sounds acceptable for part of my purposes, thanks 
to D alias syntax. But I don't know if it's enough.

Bye,
bearophile