# Frama-C-discuss mailing list archives

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# [Frama-c-discuss] floating-point examples

Claude & Virgile:
Thanks for the pointers.  Looking at the examples, it seems that most (but not all) non-trivial verifications of floating-point examples require Coq and therefore some human intervention (as opposed to being totally automated).  Would this be an accurate generalization of the state of the art at this point in time?
-Steve

On Apr 15, 2013, at 1:19 AM, Claude March? <Claude.Marche at inria.fr> wrote:

>
> See
>
> http://toccata.lri.fr/gallery/MyCosineACSL.en.html
> http://hal.inria.fr/hal-00777605
>
> - Claude
>
> Le 15/04/2013 04:48, Stephen Siegel a ?crit :
>> I'm looking for some simple, interesting floating-point examples that can be proved with Frama-C+Jessie.  Here is a good example from the ACSL manual:
>>
>> /*@ requires \abs(\exact(x)) <= 0x1p-5;
>>   @ requires \round_error(x) <= 0x1p-20;
>>   @ ensures \abs(\exact(\result) - \cos(\exact(x))) <= 0x1p-24;
>>   @ ensures \round_error(\result) <= \round_error(x) + 0x3p-24;
>>   @*/
>> float cosine(float x) {
>>   return 1.0f - x * x * 0.5f;
>> }
>>
>> However, I can't get any of the theorem provers (CVC3, Z3, Alt-Ergo, Gappa, Simplify) to prove either of the generated VCs.  (For all I know, the function may not even satisfy the contract.)  Does anyone know of any examples similar to this that can be proved, or have ideas on how to handle this example?
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>
> --
> Claude March?                          | tel: +33 1 72 92 59 69
> INRIA Saclay - ?le-de-France           |
> Universit? Paris-sud, Bat. 650         | http://www.lri.fr/~marche/
> F-91405 ORSAY Cedex                    |
>
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