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* [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double
@ 2011-02-15 0:14 dogbreath69 at hotmail dot com
2011-02-15 0:20 ` [Bug c/47742] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: dogbreath69 at hotmail dot com @ 2011-02-15 0:14 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
Summary: Large Values Increment By 1 When Casting Long to
Double
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: dogbreath69@hotmail.com
When casting some large long values to a double the resultant double values is
1 larger than the long. This can easily be seen with the value for LONG_MAX,
but will even appear with long values as low as 23372036854775807 (and possibly
lower). It is not consistent and does not affect all large longs, but does
appear in a great number of them.
ratscat> gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-libgcj-multifile
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic
--host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
Program is:
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <float.h>
int main( int argc, char **argv ) {
long infc = LONG_MAX;
double real_size = (double) infc;
printf( "infc %ld\nreal_size %lf\n", infc, real_size );
exit( 0 );
}
ratscat> gcc -Wall truncfc.c
ratscat> a.out
infc 9223372036854775807
real_size 9223372036854775808.000000
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/47742] Large Values Increment By 1 When Casting Long to Double
2011-02-15 0:14 [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double dogbreath69 at hotmail dot com
@ 2011-02-15 0:20 ` pinskia at gcc dot gnu.org
2011-02-15 23:16 ` manu at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2011-02-15 0:20 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-02-15 00:14:37 UTC ---
This is correct as long is 64bits and the precision of a double is less than
64bits.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/47742] Large Values Increment By 1 When Casting Long to Double
2011-02-15 0:14 [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double dogbreath69 at hotmail dot com
2011-02-15 0:20 ` [Bug c/47742] " pinskia at gcc dot gnu.org
@ 2011-02-15 23:16 ` manu at gcc dot gnu.org
2011-02-15 23:18 ` manu at gcc dot gnu.org
2011-02-16 6:05 ` dogbreath69 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: manu at gcc dot gnu.org @ 2011-02-15 23:16 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-02-15 23:15:03 UTC ---
I think GCC (>= 4.4) should catch this -Wconversion is you drop the forced
cast:
long infc = LONG_MAX;
double real_size = infc;
No?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/47742] Large Values Increment By 1 When Casting Long to Double
2011-02-15 0:14 [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double dogbreath69 at hotmail dot com
2011-02-15 0:20 ` [Bug c/47742] " pinskia at gcc dot gnu.org
2011-02-15 23:16 ` manu at gcc dot gnu.org
@ 2011-02-15 23:18 ` manu at gcc dot gnu.org
2011-02-16 6:05 ` dogbreath69 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: manu at gcc dot gnu.org @ 2011-02-15 23:18 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-02-15 23:16:09 UTC ---
Let me try again:
I think GCC (>= 4.4) should catch this using -Wconversion if you drop the
explicit
cast like in:
long infc = LONG_MAX;
double real_size = infc;
Doesn't it?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/47742] Large Values Increment By 1 When Casting Long to Double
2011-02-15 0:14 [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double dogbreath69 at hotmail dot com
` (2 preceding siblings ...)
2011-02-15 23:18 ` manu at gcc dot gnu.org
@ 2011-02-16 6:05 ` dogbreath69 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: dogbreath69 at hotmail dot com @ 2011-02-16 6:05 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
--- Comment #4 from dogbreath69 at hotmail dot com 2011-02-16 05:08:06 UTC ---
I haven't tried it with anything greater than GCC 4.1.2. Therefore I do not
know the answer.
> From: gcc-bugzilla@gcc.gnu.org
> To: dogbreath69@hotmail.com
> Subject: [Bug c/47742] Large Values Increment By 1 When Casting Long to Double
> Date: Tue, 15 Feb 2011 23:16:17 +0000
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47742
>
> --- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-02-15 23:16:09 UTC ---
> Let me try again:
>
> I think GCC (>= 4.4) should catch this using -Wconversion if you drop the
> explicit
> cast like in:
>
> long infc = LONG_MAX;
> double real_size = infc;
>
> Doesn't it?
>
> --
> Configure bugmail: http://gcc.gnu.org/bugzilla/userprefs.cgi?tab=email
> ------- You are receiving this mail because: -------
> You reported the bug.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2011-02-16 5:08 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-02-15 0:14 [Bug c/47742] New: Large Values Increment By 1 When Casting Long to Double dogbreath69 at hotmail dot com
2011-02-15 0:20 ` [Bug c/47742] " pinskia at gcc dot gnu.org
2011-02-15 23:16 ` manu at gcc dot gnu.org
2011-02-15 23:18 ` manu at gcc dot gnu.org
2011-02-16 6:05 ` dogbreath69 at hotmail dot com
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