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[Frama-c-discuss] using floating-point + in spec

Le 01/12/2011 11:11, Virgile Prevosto a ?crit :
> On 01/12/2011 11:02, Virgile Prevosto wrote:
>> But x (a floating point variable coming directly from C), as well as
>> \round_double(\NearestEven,y+z) could namely be infinities. It thus
>> makes sense to use \eq_float to compare them.
> Oops, I forgot something: an anonymous floating-point expert points me
> to the fact that y and z could themselves be infinity or even NaN. In
> that case, we are not able to say anything about their sum (As per ACSL
> manual, we are in fact not able to say anything about their counterpart
> in the real numbers). Thus I guess that the approach of rounding the
> result of the addition on reals only works if y and z are neither
> infinity nor NaN.

Indeed, your anonymous expert is right.

But to remain simple, assuming that the user uses the default Jessie 
mode for analyzing floating-point programs, where it is requires to show 
non-overflow, the best way to specify

x = y+z


//@ ensures x == \round_double(\NearestEven,y+z);

With the mode supporting special values, it is probably

//@ ensures \eq_float(x,\add_float(y,z));
(!*untested*!, \add_float probably not supported)

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