[rust-dev] Integer overflow, round -2147483648

John Regehr regehr at cs.utah.edu
Mon Jun 23 17:16:44 PDT 2014


> I do think Rust should exposed either `checked { }` or operators for
> checked arithmetic along with an opt-in lint to deny the unchecked
> operators. You can opt-out of a lint for a function/impl/module after
> opting into it at a higher scope.
>
> I'm just making it clear that doing this by default would make Rust
> slower than Java by default, and I think that would kill off interest in
> the language. I know I wouldn't be interested anymore.

Sure, I think there are a lot of reasonable options here, and I agree 
that speed and predictability are super important for Rust.

One thing I personally think is very important (not for 1.0, but 
eventually) is to make it possible -- no need for this to be mandatory 
-- to get overflow checking for the default integer type.  I'm happy to 
use a special compiler flag or whatever to get this.  The only 
controversial thing this requires from the core language is a way for me 
to tell the compiler which integers (a tiny subset, typically) should 
have wrapping behavior.

I realize that safe integers are available and that operator overloading 
goes a lot ways towards making these palatable, but the fact is that 
everyone is an optimist when it comes to integer overflow bugs.  People 
just do not think they're going to get bitten.

Finally, I'll note that certain optimizations such as array bounds check 
removal and some loop optimziations actually get better then integers 
cannot wrap.  Clearly we would not expect, in general, for these 
benefits to make up for the costs of overflow checking.

John


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