[PATCH 05/11] staging: comedi: core: initialize subdevice s->io_bits in postconfig

[Dan Carpenter]

On Thu, Aug 29, 2013 at 04:43:49PM +0000, Hartley Sweeten wrote:
> > You don't really need to test s->n_chan < 32.  For s->n_chan >= 32, 
> > s->io_bits will end up set to 0xffffffff anyway (and for s->n_chan > 32, 
> > the low-level drivers shouldn't really be using s->state and s->io_bits 
> > anyway).
> 
> I wasn't sure about that. 1 << 32 overflows the unsigned int to 0x100000000.
> But I guess the 32-bit portion (0x00000000) - 1 is still 0xffffffff.
> 

Nope.  Shift wrapping doesn't work like that.  Here is how it works in
GCC.

int maint(void)
{
	int a, b, shift;

	a = 1 << 32; /* a is zero */
	shift = 32;
	b = 1 << shift; /* b wraps to 1 */

	printf("%x %x\n", a, b);
}

regards,
dan carpenter