[Bug c/47473] New: Incorrect computation with complex numbers when using -std=c99

["abelk at live dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47473

           Summary: Incorrect computation with complex numbers when using
                    -std=c99
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: abelk@live.com


Created attachment 23131
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23131
complexbug3.i

This is a report about an issue encountered in MinGW GCC. The maintainers of
the MinGW project suggested to report it here.

The command line that triggers the bug is:

gcc -v -save-temps -Wall -std=c99 complexbug3.c -o complexbug3.exe

The option -std=c99 triggers the bug.

The resultant output is:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/program
files/mingw/bin/../libexec/gcc/mingw32/4.5.0/lto-wrapper.exe
Target: mingw32
Configured with: ../gcc-4.5.0/configure
--enable-languages=c,c++,ada,fortran,objc,obj-c++ --disable-sjlj-exceptions
--with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry
--enable-libstdcxx-debug --enable-version-specific-runtime-libs
--disable-werror --build=mingw32 --prefix=/mingw
Thread model: win32
gcc version 4.5.0 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c99' '-o'
'complexbug3.exe' '-mtune=i386' '-march=i386'
 c:/program files/mingw/bin/../libexec/gcc/mingw32/4.5.0/cc1.exe -E -quiet -v
-iprefix c:\program files\mingw\bin\../lib/gcc/mingw32/4.5.0/ complexbug3.c
-mtune=i386 -march=i386 -std=c99 -Wall -fpch-preprocess -o complexbug3.i
ignoring nonexistent directory "c:\program
files\mingw\bin\../lib/gcc/mingw32/4.5.0/../../../../mingw32/include"
ignoring nonexistent directory "c:/mingw/include"
ignoring nonexistent directory "/mingw/include"
ignoring duplicate directory "c:/program
files/mingw/lib/gcc/../../lib/gcc/mingw32/4.5.0/include"
ignoring duplicate directory "c:/program
files/mingw/lib/gcc/../../lib/gcc/mingw32/4.5.0/include-fixed"
ignoring nonexistent directory "c:/program
files/mingw/lib/gcc/../../lib/gcc/mingw32/4.5.0/../../../../mingw32/include"
ignoring nonexistent directory "/mingw/include"
#include "..." search starts here:
#include <...> search starts here:
 c:\program files\mingw\bin\../lib/gcc/mingw32/4.5.0/../../../../include
 c:\program files\mingw\bin\../lib/gcc/mingw32/4.5.0/include
 c:\program files\mingw\bin\../lib/gcc/mingw32/4.5.0/include-fixed
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c99' '-o'
'complexbug3.exe' '-mtune=i386' '-march=i386'
 c:/program files/mingw/bin/../libexec/gcc/mingw32/4.5.0/cc1.exe -fpreprocessed
complexbug3.i -quiet -dumpbase complexbug3.c -mtune=i386 -march=i386 -auxbase
complexbug3 -Wall -std=c99 -version -o complexbug3.s
GNU C (GCC) version 4.5.0 (mingw32)
    compiled by GNU C version 4.5.0, GMP version 5.0.1, MPFR version 2.4.1, MPC
version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (GCC) version 4.5.0 (mingw32)
    compiled by GNU C version 4.5.0, GMP version 5.0.1, MPFR version 2.4.1, MPC
version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 6773400e8bc9df4b012089071ac4c86b
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c99' '-o'
'complexbug3.exe' '-mtune=i386' '-march=i386'
 c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../../mingw32/bin/as.exe -o
complexbug3.o complexbug3.s
COMPILER_PATH=c:/program
files/mingw/bin/../libexec/gcc/mingw32/4.5.0/;c:/program
files/mingw/bin/../libexec/gcc/;c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../../mingw32/bin/
LIBRARY_PATH=c:/program files/mingw/bin/../lib/gcc/mingw32/4.5.0/;c:/program
files/mingw/bin/../lib/gcc/;c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../../mingw32/lib/;c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c99' '-o'
'complexbug3.exe' '-mtune=i386' '-march=i386'
 c:/program files/mingw/bin/../libexec/gcc/mingw32/4.5.0/collect2.exe -Bdynamic
-o complexbug3.exe c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../crt2.o c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/crtbegin.o -Lc:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0 -Lc:/program
files/mingw/bin/../lib/gcc -Lc:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../../mingw32/lib -Lc:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/../../.. complexbug3.o -lmingw32
-lgcc_eh -lgcc -lmoldname -lmingwex -lmsvcrt -luser32 -lkernel32 -ladvapi32
-lshell32 -lmingw32 -lgcc_eh -lgcc -lmoldname -lmingwex -lmsvcrt c:/program
files/mingw/bin/../lib/gcc/mingw32/4.5.0/crtend.o


The result of executing complexbug3.exe is mathematically incorrect:
(0.2 - I*0.3)*(0.3 - I*0.9) = (0.06, -0.09)