[Bug c/19765] New: GCC math operations can fail with type double

[gcc-bugzilla at gcc dot gnu dot org]

        simple subtraction works for small values of doubles, but fails for 
larger values

TEST CODE FOLLOWS:
int main (int argc, char **argv)
{
        double n1, n2;

        n1=74925983.0;

        n2=n1-1;
        if (n1==n2) printf ("BUG: the numbers are equal.\n");
        else printf ("NO BUG: the numbers are different\n");

        n1=3275892374984327984327498274925983.0;

        n2=n1-1;
        if (n1==n2) printf ("BUG: the numbers are equal.\n");
        else printf ("NO BUG: the numbers are different\n");

        return (0);
}

COMPILE WITH: gcc -o test test.c
EXECUTE: ./test

Environment:
System: Linux bubbles 2.6.11-rc1 #1 SMP Thu Jan 27 02:57:53 MST 2005 i686 
Intel(R) Pentium(R) 4 CPU 2.80GHz GenuineIntel GNU/Linux
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: /var/tmp/portage/gcc-3.3.3-r6/work/gcc-3.3.3/configure 
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.3 
--includedir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.3/include 
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3 
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3/man 
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.3/info --enable-shared 
--host=i686-pc-linux-gnu --target=i686-pc-linux-gnu --with-system-zlib 
--enable-languages=c,c++ --enable-threads=posix --enable-long-long 
--disable-checking --disable-libunwind-exceptions --enable-cstdio=stdio 
--enable-version-specific-runtime-libs 
--with-gxx-include-dir=/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.3/include/g++-v3 
--with-local-prefix=/usr/local --enable-shared --enable-nls 
--without-included-gettext --disable-multilib --enable-__cxa_atexit 
--enable-clocale=generic

How-To-Repeat:
        The test program shows when the bug does/doesnt occur.
------- Additional Comments From nelson at bubbles dot reversion dot ccn  
2005-02-02 17:05 -------
Fix:
        I dont know how to fix this.

-- 
           Summary: GCC math operations can fail with type double
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: nelson at bubbles dot reversion dot ccn
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19765