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From: "paul dot richard dot thomas at cea dot fr" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/24518] New: Intrinsic MOD incorrect for large arg1/arg2 and slow. Date: Tue, 25 Oct 2005 13:21:00 -0000 [thread overview] Message-ID: <bug-24518-9236@http.gcc.gnu.org/bugzilla/> (raw) This: real*8 :: x = 10.0e9 do i = 10, 22 x = 10d0 * x print '(a,i2,a,g14.8)', "mod (10**",i,", 1.7_8) = ",mod (x, 1.7_8) end do end does this with cvs gfortran mod (10**10, 1.7_8) = 1.3000026 mod (10**11, 1.7_8) = 1.1000261 mod (10**12, 1.7_8) = 0.80026150 mod (10**13, 1.7_8) = 1.2026138 mod (10**14, 1.7_8) = 0.12609863 mod (10**15, 1.7_8) = 1.2607422 mod (10**16, 1.7_8) = 5.8125000 mod (10**17, 1.7_8) = -50.687500 mod (10**18, 1.7_8) = 364.00000 mod (10**19, 1.7_8) = -.70000000E+20 mod (10**20, 1.7_8) = -.70000000E+21 mod (10**21, 1.7_8) = -.70000000E+22 mod (10**22, 1.7_8) = -.70000000E+23 and this with a leading commercial brand: mod (10**10, 1.7_8) = 1.3000026 mod (10**11, 1.7_8) = 1.1000261 mod (10**12, 1.7_8) = 0.80026123 mod (10**13, 1.7_8) = 1.2026123 mod (10**14, 1.7_8) = 0.12612289 mod (10**15, 1.7_8) = 1.2612289 mod (10**16, 1.7_8) = 0.71228947 mod (10**17, 1.7_8) = 0.32289470 mod (10**18, 1.7_8) = 1.5289470 mod (10**19, 1.7_8) = 1.6894697 mod (10**20, 1.7_8) = 1.5946971 mod (10**21, 1.7_8) = 0.64697063 mod (10**22, 1.7_8) = 0.86970625 gfortran loses it at around 10**16 and starts producing values larger than the second argument. Whilst, to some degree, one deserves to be hit on the nose for trying to calculate mod for these values, a slightly less deviant behaviour might be better. As noted in the list http://gcc.gnu.org/ml/fortran/2005-10/msg00482.html, this leading brand is about twice as fast in calulating mod, as gfortran, in spite of its apparently using 64 bit arithmetic. -- Summary: Intrinsic MOD incorrect for large arg1/arg2 and slow. Product: gcc Version: 4.1.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: paul dot richard dot thomas at cea dot fr http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24518
next reply other threads:[~2005-10-25 13:21 UTC|newest] Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top 2005-10-25 13:21 paul dot richard dot thomas at cea dot fr [this message] 2005-10-25 14:37 ` [Bug fortran/24518] " pinskia at gcc dot gnu dot org 2006-06-20 12:44 ` fxcoudert at gcc dot gnu dot org 2006-06-21 8:04 ` paul dot richard dot thomas at cea dot fr 2006-10-22 21:01 ` fxcoudert at gcc dot gnu dot org 2006-10-23 6:19 ` fxcoudert at gcc dot gnu dot org 2006-10-25 7:34 ` uros at kss-loka dot si 2006-10-25 8:19 ` fxcoudert at gcc dot gnu dot org 2006-10-25 11:49 ` uros at kss-loka dot si 2006-10-25 13:53 ` fxcoudert at gcc dot gnu dot org 2006-10-25 14:16 ` uros at kss-loka dot si 2006-10-26 4:04 ` sgk at troutmask dot apl dot washington dot edu 2006-10-26 20:09 ` pault at gcc dot gnu dot org 2006-10-26 22:22 ` uros at kss-loka dot si 2006-10-31 15:56 ` pault at gcc dot gnu dot org 2006-10-31 16:06 ` fxcoudert at gcc dot gnu dot org 2006-10-31 16:14 ` paul dot richard dot thomas at cea dot fr 2006-10-31 16:21 ` pault at gcc dot gnu dot org 2006-10-31 16:47 ` fxcoudert at gcc dot gnu dot org 2006-11-05 6:28 ` pault at gcc dot gnu dot org 2006-11-05 8:46 ` pault at gcc dot gnu dot org 2006-11-05 22:18 ` pault at gcc dot gnu dot org 2006-11-10 21:53 ` pault at gcc dot gnu dot org 2006-12-01 0:09 ` chaoyingfu at gcc dot gnu dot org 2006-12-02 8:12 ` ebotcazou at gcc dot gnu dot org 2006-12-02 8:23 ` burnus at gcc dot gnu dot org 2006-12-02 8:28 ` pinskia at gcc dot gnu dot org
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