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* c/7949: Mishandled double != 0.0 at -O1
@ 2002-09-17 7:06 Ake.Sandgren
0 siblings, 0 replies; only message in thread
From: Ake.Sandgren @ 2002-09-17 7:06 UTC (permalink / raw)
To: gcc-gnats, debian-gcc
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>Number: 7949
>Category: c
>Synopsis: Mishandling of double != 0.0 at -O1
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Tue Sep 17 07:06:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Åke Sandgren
>Release: 3.2.1 20020830 (Debian prerelease) (Debian testing/unstable)
>Organization:
HPC2N, Umeå University, Sweden
>Environment:
System: Linux y-boda.hpc2n.umu.se 2.4.18.dell.i8k.5 #1 Fri Jun 7 11:15:41 CEST 2002 i686 unknown
Architecture: i686
host: i386-pc-linux-gnu
build: i386-pc-linux-gnu
target: i386-pc-linux-gnu
configured with: /mnt/data/gcc-3.1/gcc-3.2-3.2.1ds0/src/configure -v --enable-languages=c,c++,java,f77,proto,objc,ada --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.2 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --enable-__cxa_atexit --enable-java-gc=boehm --enable-objc-gc i386-linux
>Description:
The following code gives different results with -O0 and -O1/2 on x86
machines.
It works (with the relevant bigendian change) on sparc solaris8.
gcc 2.95.4 gives correct output at all -O levels.
gcc-3.[01] gives the same error as 3.2
This is IEEE correct code.
>How-To-Repeat:
double rvals(int v)
{
union a {
double d;
unsigned int i[2];
} aa;
if (v == 0) {
/* Return maximum double */
/* For bigendian machines swap i[0] and i[1] */
aa.i[0] = 0xffffffff;
aa.i[1] = 0x7fefffff;
} else {
/* Return minimum double */
/* For bigendian machines swap i[0] and i[1] */
aa.i[0] = 0;
aa.i[1] = 0x100000;
}
return aa.d;
}
main()
{
double rmax, rmin, inf, zero;
union a {
double d;
unsigned int i[2];
} aa;
rmax = rvals(0);
rmin = rvals(1);
inf = rmax / rmin;
zero = 1.0 / inf;
if (zero != 0.0) {
printf("ERROR\n");
aa.d = rmax;
printf("rmax: i[0] = %x, i[1] = %x\n", aa.i[0], aa.i[1]);
aa.d = rmin;
printf("rmin: i[0] = %x, i[1] = %x\n", aa.i[0], aa.i[1]);
aa.d = inf;
printf("inf: i[0] = %x, i[1] = %x\n", aa.i[0], aa.i[1]);
aa.d = zero;
printf("zero: i[0] = %x, i[1] = %x\n", aa.i[0], aa.i[1]);
} else {
printf("This works.\n");
}
}
# gcc-3.2 -O0 -o bug gcc.bug.c
# ./bug
This works.
# gcc-3.2 -O1 -o bug gcc.bug.c
# ./bug
ERROR
rmax: i[0] = ffffffff, i[1] = 7fefffff
rmin: i[0] = 0, i[1] = 100000
inf: i[0] = 0, i[1] = 7ff00000
zero: i[0] = 0, i[1] = 0
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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2002-09-17 7:06 c/7949: Mishandled double != 0.0 at -O1 Ake.Sandgren
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