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

  • Subject: [Frama-c-discuss] using floating-point + in spec
  • From: virgile.prevosto at cea.fr (Virgile Prevosto)
  • Date: Thu, 01 Dec 2011 09:04:55 +0100
  • In-reply-to: <5F048F9B-D8E6-4560-9DEF-38BF8571608D@UDel.Edu>
  • References: <5F048F9B-D8E6-4560-9DEF-38BF8571608D@UDel.Edu>
Hello,

On 30/11/2011 23:22, Stephen Siegel wrote:
> What is the right way to use floating-point addition in a specification?  For example, I want to say
>
> ensures x == y + z;
>
> where x, y, and z are variables in the program, and I want the "+" to mean "floating-point addition" (i.e., whatever the "+" means inside the program), not "real (mathematical) addition".
>

If I'm not mistaken, addition on floating-point values is defined by 
IEEE754 as rounding the result of the addition on the corresponding real 
number. Thus, your ensures clause could be expressed (assuming x,y and z 
are double and rounding mode is nearest even. The various other 
possibilities are described in ACSL manual, section 2.2.5) as

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

NB: the \eq_double function is unimplemented in the current version of 
Frama-C.

Hope this helps,
-- 
E tutto per oggi, a la prossima volta
Virgile