Re: Bash arithmetic doesn't give error message on wrap.

[Andreas Schwab]

prj@po.cwru.edu (Paul Jarc) writes:

> Richard Neill <rn214@hermes.cam.ac.uk> wrote:
>> I thought testing for overflow was quite simple?
>> Isn't it just a case of looking at the carry-bit, and seeing whether it 
>> gets set?
>
> That's usually how it's done in assembly.  In C, it's somewhat more
> compilcated.  For example:
> result=a*b;
> if (result/a!=b) { report overflow; }

That won't work, since (signed integer) overflow is undefined in C.  A
compiler is allowed to optimize the condition to false.

Andreas.

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Andreas Schwab, SuSE Labs, schwab@suse.de
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