[Bug target/15852] issues related to floating point precision

[sliwa at cft dot edu dot pl]

------- Additional Comments From sliwa at cft dot edu dot pl  2004-06-08 18:51 -------
Subject: Re:  issues related to floating point precision


On Sun, Jun 06, 2004 at 07:35:12PM -0000, jsm at polyomino dot org dot uk wrote:
> 
> ------- Additional Comments From jsm at polyomino dot org dot uk  2004-06-06 19:35 -------
> Subject: Re:  issues related to floating point precision
> 
> On Sun, 6 Jun 2004, pinskia at gcc dot gnu dot org wrote:
> 
> > Not a bug, read the references in bug 323.
> 
> You mean "known bug", not "not a bug".  Excess precision is allowed by
> C99, and you can even define FLT_EVAL_METHOD to -1 to say that it's

What about fortran and the comparison issues? It seems that the Intel
compiler takes care of them. Consider this example:

//assume that
float x=0.4, y=0.1; // I mean float values!
//then let
float z=x+y;
//then this is true with -ffloat-store,
// bacause z is chopped to 0.5, whereas x+y not:
if(x+y > z)
  printf("not good...\n");


This issue is the reason for a failure with BLAS test.

BTW, being within the standards does not mean being useful.

Regards,
C.S.


> indeterminate when there's excess precision (which at present it is, given
> that spills reduce excess precision unpredictably), but we define
> FLT_EVAL_METHOD to 2 on x86 (saying that expressions are predictably
> evaluated as long double), and even with -ffloat-store we don't follow the
> standard rules that conversions to the same or narrower type (by
> assignment, cast and (probably) function call and return) get rid of
> excess precision (but note that conversions of float to double don't get
> rid of excess precision even if the float is being stored with the
> precision of long double).  That we don't get rid of excess precision on
> casts is clearly a bug, as is the bad definition of FLT_EVAL_METHOD.
> 
> 
> 
> -- 
> 
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15852
> 
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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15852