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From: long@stsci.edu To: gcc-gnats@gcc.gnu.org Subject: c/5277: NaN unexpectedly Date: Fri, 04 Jan 2002 11:06:00 -0000 [thread overview] Message-ID: <20020104190205.28407.qmail@sources.redhat.com> (raw) >Number: 5277 >Category: c >Synopsis: NaN unexpectedly >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: sw-bug >Submitter-Id: net >Arrival-Date: Fri Jan 04 11:06:00 PST 2002 >Closed-Date: >Last-Modified: >Originator: Knox S. Long >Release: gcc-2.96-81 >Organization: >Environment: Redhat 7.1 (on a Dell Dimension 1 Ghz machine) glibc-2.2.4-19.3 >Description: I am seeing a problem in which simple double precision math occasionally generates NAN problems. The probalem is odd because if on printf's the offending variable, and reprints the result, the NAN problem goes away Here is an example code fragement where this can occur. double thierry_velocity (x, v) double x[]; double v[]; { int n; double r, speed; double frac,z; double length (); z=x[0]*x[0]+x[1]*x[1]+x[2]*x[2]; if(sane_check(z)){ printf("%f\n",z); z=x[0]*x[0]+x[1]*x[1]+x[2]*x[2]; printf("%f\n",z); } r = length (x); ... where sane_check simply checks to see whether x is finite, e.g. int sane_check (x) double x; { int i; if ((i = finite (x)) == 0) { Error ("sane_check: %d %e\n", i, x); return (-1); } return (0); } There was some discussion of a similar problem on the web associated with gcc 2.95.1. and even a reference to a bug report which I could not locate. I ran the identical program on a Sun (with gcc 2.95) and did not see the problem. >How-To-Repeat: >Fix: >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2002-01-04 19:06 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-01-04 11:06 long [this message] 2002-01-06 10:36 Knox S. Long 2002-11-05 7:59 bangerth
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