Re: gcc strangeness
Hi, re:
>one of my friends has raisen very strange issue regarding gcc rounding:
> printf("%f %.3f %d\n", a*100, a*100, (int)(a*100));
>
> 9.99 10.000 9
Hasty unresearched guess:
If you print with a large fp fmt (say 22.18)
you will get a better idea of the value:
9.99403953552246 10.000 9
The "%.3f" says to round upward to inf after 3 decimal
places, so "9." is rounded to "10.000".
The "%f" defaults to round up after 6 decimal places,
so "9.994" is rounded to ""9.99".
Everything is working.
There are a lot of subtleties in floating-point
printf(). Printing binary values out and reading them
back accurately can be a non-trivial exercise.
- bruce
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Re: gdb 6.1.1: File format not recognized
Use gdb6 from the ports. gdb6 -k . --WjW - Original Message - From: "Matthias Schuendehuette" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, July 10, 2004 8:36 PM Subject: gdb 6.1.1: File format not recognized > Hello, > > I tried to look into a core dump from a -current kernel with > 'gdb' but all i get is: > > --8><- > [EMAIL PROTECTED] - /var/crash > 504 # gdb kernel.debug vmcore.0 > GNU gdb 6.1.1 [FreeBSD] > Copyright 2004 Free Software Foundation, Inc. > GDB is free software, covered by the GNU General Public License, and you are > welcome to change it and/or distribute copies of it under certain conditions. > Type "show copying" to see the conditions. > There is absolutely no warranty for GDB. Type "show warranty" for details. > This GDB was configured as "i386-marcel-freebsd"... > "/var/crash/vmcore.0" is not a core dump: File format not recognized > (gdb) quit > --8><- > > I looked at the man-pages of gdb(1), savecore(8) and into the > 'Developers Handbook' but I didn't find anything about the > correct file format of a core dump. > > If I look at /var/crash/info.0, there's: > > --8><- > Good dump found on device /dev/da0s1b > Architecture: i386 > Architecture version: 1 > Dump length: 268369920B (255 MB) > Blocksize: 512 > Dumptime: Sat Jul 10 19:40:30 2004 > Hostname: current.best-eng.de > Versionstring: FreeBSD 5.2-CURRENT #5: Sat Jul 10 12:37:27 CEST 2004 > [EMAIL PROTECTED]:/raid/obj/usr/src/sys/CURRENT > Panicstring: unmount: dangling vnode > Bounds: 0 > --8><- > > Did I overlook something? Has someone a pointer or hint for me? > > > -- > Ciao/BSD - Matthias > > Matthias Schuendehuette , Berlin (Germany) > PGP-Key at and ID: 0xDDFB0A5F > ___ > [EMAIL PROTECTED] mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "[EMAIL PROTECTED]" > > ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: gcc strangeness
On Sun, 11 Jul 2004, Dimitry Andric wrote: DA> > 1.00 1.000 0 DA> > 2.00 2.000 1 DA> > 3.00 3.000 2 DA> > 4.00 4.000 3 DA> > 5.00 5.000 5 DA> > 6.00 6.000 6 DA> > 7.00 7.000 7 DA> > 8.00 8.000 7 DA> > 9.00 9.000 8 DA> > 9.99 10.000 9 DA> DA> Yes, this is completely normal if you use IEEE floating point, due to DA> decimal <-> binary conversion and other accumulating rounding errors. DA> In other words, floating point calculations will almost never be DA> exact... DA> DA> This is not a gcc problem. In fact, I can even reproduce your output DA> under Windows using a Microsoft C compiler! :) Wow, it's interesting for us to have exact step-by-step instructions for that! ;) Sincerely, D.Marck [DM5020, MCK-RIPE, DM3-RIPN] *** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- [EMAIL PROTECTED] *** ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: gcc strangeness
On 2004-07-11 at 19:06:32 Dmitry Morozovsky wrote: > 1.00 1.000 0 > 2.00 2.000 1 > 3.00 3.000 2 > 4.00 4.000 3 > 5.00 5.000 5 > 6.00 6.000 6 > 7.00 7.000 7 > 8.00 8.000 7 > 9.00 9.000 8 > 9.99 10.000 9 Yes, this is completely normal if you use IEEE floating point, due to decimal <-> binary conversion and other accumulating rounding errors. In other words, floating point calculations will almost never be exact... This is not a gcc problem. In fact, I can even reproduce your output under Windows using a Microsoft C compiler! :) pgpniUit3rNUP.pgp Description: PGP signature
gcc strangeness
Dear colleagues,
one of my friends has raisen very strange issue regarding gcc rounding:
[EMAIL PROTECTED]:/tmp/tsostik> uname -r
4.10-STABLE
[EMAIL PROTECTED]:/tmp/tsostik> gcc -v
Using builtin specs.
gcc version 2.95.4 20020320 [FreeBSD]
[EMAIL PROTECTED]:/tmp/tsostik> cat x.c
#include
int main ()
{
float a;
for(a=0.01;a<=0.1; a+=0.01)
printf("%f %.3f %d\n", a*100, a*100, (int)(a*100));
return 0;
}
[EMAIL PROTECTED]:/tmp/tsostik> cc x.c
[EMAIL PROTECTED]:/tmp/tsostik> ./a.out
1.00 1.000 0
2.00 2.000 1
3.00 3.000 2
4.00 4.000 3
5.00 5.000 5
6.00 6.000 6
7.00 7.000 7
8.00 8.000 7
9.00 9.000 8
9.99 10.000 9
Any comments?
Sincerely,
D.Marck [DM5020, MCK-RIPE, DM3-RIPN]
*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- [EMAIL PROTECTED] ***
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gdb 6.1.1: File format not recognized
Hello, I tried to look into a core dump from a -current kernel with 'gdb' but all i get is: --8><- [EMAIL PROTECTED] - /var/crash 504 # gdb kernel.debug vmcore.0 GNU gdb 6.1.1 [FreeBSD] Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-marcel-freebsd"... "/var/crash/vmcore.0" is not a core dump: File format not recognized (gdb) quit --8><- I looked at the man-pages of gdb(1), savecore(8) and into the 'Developers Handbook' but I didn't find anything about the correct file format of a core dump. If I look at /var/crash/info.0, there's: --8><- Good dump found on device /dev/da0s1b Architecture: i386 Architecture version: 1 Dump length: 268369920B (255 MB) Blocksize: 512 Dumptime: Sat Jul 10 19:40:30 2004 Hostname: current.best-eng.de Versionstring: FreeBSD 5.2-CURRENT #5: Sat Jul 10 12:37:27 CEST 2004 [EMAIL PROTECTED]:/raid/obj/usr/src/sys/CURRENT Panicstring: unmount: dangling vnode Bounds: 0 --8><- Did I overlook something? Has someone a pointer or hint for me? -- Ciao/BSD - Matthias Matthias Schuendehuette , Berlin (Germany) PGP-Key at and ID: 0xDDFB0A5F ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
