[Bug c/31166] New: Integer hex constant does not follow promoting rules

[roberto dot gordo at gmail dot com]

Forgive me if this is reported/fixed already; after many consecutive hours of
debugging I currently do not have the courage to search through the list of
bugs.

Please, try this code (tested on 32bit GNU/Linux), compiled with:
gcc -std=c99 -Wall -Wextra -o wtf wtf.c

#include <stdio.h>

int main(void)
{
        int n1, n2;
        long long n3, n4;

        n1 = -0x80000000;
        n2 = -2147483648;

        n3 = -0x80000000;
        n4 = -2147483648;

        printf("n1 = %d\n", n1);
        printf("n2 = %d\n", n2);

        printf("n3 = %lld\n", n3);
        printf("n4 = %lld\n", n4);

        return 0;
}

It consists of two int variables and two long long variables, all of them set
to the same value (-2147483648 == 0x80000000). This is what I get:

n1 = -2147483648
n2 = -2147483648
n3 = 2147483648
n4 = -2147483648

What happened to n3? It appears that hex constants are not promoted to long
long the same way as decimal ones. AFAIK, this behavoir does not match C99
(neither C90).

When compiling without -std=c99, gcc gives this warning:
warning: this decimal constant is unsigned only in ISO C90

I think that gcc is trying to say that the constant does not fit on an int (nor
a long) and it is promoted to unsigned, as it is stated by ISO C90. But yes, it
should fit on an int, because -2147483648 >= INT_MIN in this architecture.
Anyway, it is even more funny, because the warning is only for n2 and n4
(decimal constants) but not for n1 nor n4 (hex constants). This is the output
without -std=c99:

n1 = -2147483648
n2 = -2147483648
n3 = 2147483648
n4 = 2147483648

Tested with these versions of gcc:

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --with-tune=i686
--enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.0 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-awt=gtk-default --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr
--disable-werror --with-tune=pentium4 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)


-- 
           Summary: Integer hex constant does not follow promoting rules
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: roberto dot gordo at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31166