Bug 14367

A floating point calculation returns different results when performed in a
class's *= method vs. in main().  I'm not sure if the *= method is special, but
that's where it shows up.  The inconsistency is triggered by particular values
used in the calculation. 

I've seen this behavior in 3.3.3, and 3.2.3.  It does not appear in 3.1.
I've seen the behavior in the Debain (unstable) version of 3.3.3, as well as in
a personally compiled version of 3.2.3.  The resultant compiled code exhibits
the inconsistency on an AthlonMP, an Athlon, and an Intel Xeon.


At the end of this message is a uuencoded preprocessed program which exhibits
the behavior.  The code prints out the input and resultant values for the
calculation as done in the *= method and in main.  The resultant values should
be the same, but differ.  On my machines, here's the output:

1> 1582081461419629824 = 1804289383 * 1681692777 - 846930886 * 1714636915
2> 1582081461419630080 = 1804289383 * 1681692777 - 846930886 * 1714636915
1 != 2

The second value is the correct one.


malaise% /usr/bin/g++ -v -save-temps -O2 std_complex_dbl.cc -o std_complex_dbl
Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.3/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib
--enable-nls --without-included-gettext --enable-__cxa_atexit
--enable-clocale=gnu --enable-debug --enable-java-gc=boehm
--enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.3 (Debian)
 /usr/lib/gcc-lib/i486-linux/3.3.3/cc1plus -E -D__GNUG__=3 -quiet -v
-D__GNUC__=3 -D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=3 -D_GNU_SOURCE
std_complex_dbl.cc -O2 std_complex_dbl.ii
ignoring nonexistent directory "/usr/i486-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/3.3
 /usr/include/c++/3.3/i486-linux
 /usr/include/c++/3.3/backward
 /usr/local/include
 /usr/lib/gcc-lib/i486-linux/3.3.3/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/i486-linux/3.3.3/cc1plus -fpreprocessed std_complex_dbl.ii
-quiet -dumpbase std_complex_dbl.cc -auxbase std_complex_dbl -O2 -version -o
std_complex_dbl.s
GNU C++ version 3.3.3 (Debian) (i486-linux)
        compiled by GNU C version 3.3.3 (Debian).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
 as -V -Qy -o std_complex_dbl.o std_complex_dbl.s
GNU assembler version 2.14.90.0.7 (i386-linux) using BFD version 2.14.90.0.7
20031029 Debian GNU/Linux
 /usr/lib/gcc-lib/i486-linux/3.3.3/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o std_complex_dbl
/usr/lib/gcc-lib/i486-linux/3.3.3/../../../crt1.o
/usr/lib/gcc-lib/i486-linux/3.3.3/../../../crti.o
/usr/lib/gcc-lib/i486-linux/3.3.3/crtbegin.o -L/usr/lib/gcc-lib/i486-linux/3.3.3
-L/usr/lib/gcc-lib/i486-linux/3.3.3/../../.. std_complex_dbl.o -lstdc++ -lm
-lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc-lib/i486-linux/3.3.3/crtend.o
/usr/lib/gcc-lib/i486-linux/3.3.3/../../../crtn.o

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