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From: "sliwa at cft dot edu dot pl" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/15852] issues related to floating point precision Date: Tue, 08 Jun 2004 18:51:00 -0000 [thread overview] Message-ID: <20040608185135.16697.qmail@sourceware.org> (raw) In-Reply-To: <20040606180702.15852.sliwa@theta1.cft.edu.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 > > ------- You are receiving this mail because: ------- > You reported the bug, or are watching the reporter. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15852
prev parent reply other threads:[~2004-06-08 18:51 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2004-06-06 18:07 [Bug target/15852] New: " sliwa at theta1 dot cft dot edu dot pl 2004-06-06 18:13 ` [Bug target/15852] " pinskia at gcc dot gnu dot org 2004-06-06 19:35 ` jsm at polyomino dot org dot uk 2004-06-08 18:51 ` sliwa at cft dot edu dot pl [this message]
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