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Top Forums Programming Strange value of the double type variable: -nan(0x8000000000000) Post 302903832 by 915086731 on Friday 30th of May 2014 03:25:22 AM
Old 05-30-2014
Strange value of the double type variable: -nan(0x8000000000000)

I am confused by the value of "currdisk->currangle" after adding operation. Initially the value of "currdisk->currangle" is 0.77500000000000013, but after adding operation, it's changed to "-nan(0x8000000000000)", Can anyone explain ? Thanks! The following is the occasion of gdb debugging.

Code:
3338          currdisk->currangle += (simtime - seg->time) / currdisk->rotatetime;
(gdb) p currdisk->currangle
$28 = 0.77500000000000013
(gdb) p (simtime - seg->time) / currdisk->rotatetime
$29 = 0.00833333333333325
(gdb) p (simtime - seg->time) 
$30 = 0.092592592592591672
(gdb) p currdisk->rotatetime
$31 = 11.111111111111111
(gdb) n

(gdb) p currdisk->currangle 
$32 = -nan(0x8000000000000)
(gdb) p/x (char[8])currdisk->currangle 
$52 = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xf8, 0xff}
(gdb)

Then I change
currdisk->currangle += (simtime - seg->time) / currdisk->rotatetime ;
to
double tmp1 = (simtime - seg->time) / currdisk->rotatetime;
currdisk->currangle += tmp1;

The value of currdisk->currangle is normal. Can anyone explain the confusing phenomenon ?

---------- Post updated 05-30-14 at 02:25 AM ---------- Previous update was 05-29-14 at 10:56 PM ----------

All are double type.
 

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BTRACEBACK(1)					     Network backup, recovery and verification					     BTRACEBACK(1)

NAME
btraceback - wrapper script around gdb and bsmtp SYNOPSIS
btraceback /path/to/binary pid DESCRIPTION
btraceback is a wrapper shell script around the gdb debugger (or dbx on Solaris systems) and bsmtp, provided for debugging purposes. USAGE
btraceback is called by the exception handlers of the Bacula daemons during a crash. It can also be called interactively to view the cur- rent state of the threads belonging to a process, but this is not recommended unless you are trying to debug a problem (see below). NOTES
In order to work properly, debugging symbols must be available to the debugger on the system, and gdb, or dbx (on Solaris systems) must be available in the $PATH. If the Director or Storage daemon runs under a non-root uid, you will probably need to be modify the btraceback script to elevate privi- leges for the call to gdb/dbx, to ensure it has the proper permissions to debug when called by the daemon. Although Bacula's use of btraceback within its exception handlers is always safe, manual or interactive use of btraceback is subject to the same risks than live debugging of any program, which means it could cause Bacula to crash under rare and abnormal circumstances. Conse- quently we do not recommend manual use of btraceback in production environments unless it is required for debugging a problem. ENVIRONMENT
btracback relies on $PATH to find the debugger. FILES
/usr/lib/bacula/btraceback The script itself. /usr/sbin/btraceback symbolic link to /usr/lib/bacula/btraceback /etc/bacula/scripts/btraceback.gdb the GDB command batch used to output a stack trace AUTHOR
This manual page was written by Lucas B. Cohen <lbc@members.fsf.org> SEE ALSO
bsmtp(1) Kern Sibbald 6 December 2009 BTRACEBACK(1)
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