Ah this just demonstrates the bit loss. Here is an example using 2 different width ints:

use Inline C => <<'EOC';

void poo () {
    unsigned short s = 0xffff;
    unsigned long  l = (unsigned long) s;
    printf("short %08x\n long %08x\n", sizeof(s), sizeof(l));
    printf("short %08x\n long %08x\n", s, l);
    s <<= 4; l <<= 4;
    printf("short %08x\n long %08x\n", s, l);
    s >>= 4; l >>= 4;
    printf("short %08x\n long %08x\n", s, l);
    if ( l != (unsigned long) s ) 
        printf("Bugger!\nerror %08x\n", l^(unsigned long)s );
}

EOC

poo();

__END__
short 00000002
 long 00000004
short 0000ffff
 long 0000ffff
short 0000fff0
 long 000ffff0
short 00000fff
 long 0000ffff
Bugger!
error 0000f000
[download]

This is exactly what happens if you think you have a 32 bit int but actually have a 64 bit int. 2 operations and the results now differ.....