On Fri, Sep 7, 2012 at 10:57 AM, <paul_kon...@dell.com> wrote:
> This seems to be a bug:
>
> struct bug
> {
> int f1:1;
> unsigned long long f2:31;
> };
>
> struct bug test = { 1, 0x8000ULL };
>
> int main (int c, char **v)
> {
> unsigned long long tf2;
>
> tf2 = test.f2 << 16;
> if (tf2 == 0x80000000ULL)
> return 0;
> return 1;
> }
>
> Since the underlying type of field f2 is unsigned long long, I would not
> expect the expression "test.f2 << 16" to do sign extending of a 32 bit
> intermediate result. But that is in fact what GCC produces, for x86_64-linux
> (gcc 4.7.0).
>
> If I explicitly cast test.f2 to unsigned long long before the shift, the
> expected result appears. But I shouldn't have to do that cast, given that
> the type of f2 is already unsigned long long, correct?
The type of "test.f2" is a 31 bit unsigned integer (the declared type
is used for alignment) and that fits in a 32bit signed integer so when
doing test.f2 << 16, it is promoted to only an 32bit signed integer.
Thanks,
Andrew
>
> paul
>
