test.cxx
------------------------------------------------------
#include <iostream>

struct A
{
    unsigned short x:14;
    unsigned short y:14;
};


extern unsigned n;

int main()
{
    A a;

    a.x = n & 0x3FFF;
    a.y = (n>>14) & 0x3FFF;

    unsigned expected = n & 0x3FFF;

    if( a.x != expected )
    {
        std::cout << "test failed: "
            << " (x=" << a.x
            << ") != " << expected
            << ", y=" << a.y
            << std::endl;
        return 1;
    }

    std::cout << "test succedeed" << std::endl;

    return 0;
}

unsigned n = 0xFE7B4873U;
------------------------------------------------------

output:
test failed:  (x=18547) != 2163, y=14829

14-bit unsigned field expands with non-zero padding bits


appears with gcc-4.2.1, gcc-4.1.2, gcc-4.2-20070822
does not appear with gcc-3.4.6

gcc was configured and built with crosstool-0.43 (with glibc-2.3.2)

powerpc-603-linux-gnu-g++ -v
Using built-in specs.
Target: powerpc-603-linux-gnu
Configured with: /home/corpse/tmp/interlink/crosstool-0.43/build/powerpc-603-linux-gnu/gcc-4.2.1-glibc-2.3.2/gcc-4.2.1/configure --target=powerpc-603-linux-gnu --host=i686-host_pc-linux-gnu --prefix=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu --with-cpu=603 --enable-cxx-flags=-mcpu=603 --with-headers=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu/powerpc-603-linux-gnu/include --with-local-prefix=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu/powerpc-603-linux-gnu --disable-nls --enable-threads=posix --enable-symvers=gnu --enable-__cxa_atexit --enable-languages=c,c++ --enable-shared --enable-c99 --enable-long-long
Thread model: posix
gcc version 4.2.1