On Mon, Aug 06, 2001 at 11:04:38AM -0700, Steven Liu wrote:
> extern __inline__ void set_bit(int nr, void * addr)
> {
> int mask;
> int *a = addr;
> __bi_flags;
>
> a += nr >> 5; // <---- why shits right 5
> bits?
> mask = 1 << (nr & 0x1f);
> __bi_save_flags(flags);
> __bi_cli();
> *a |= mask;
> __bi_restore_flags(flags);
> }
>
> In
>
> extern __inline__ int test_bit(int nr, const void *addr)
> {
> return ((1UL << (nr & 31)) & (((const unsigned int *) addr)[nr
> >> 5])) != 0;
> }
>
> addr is always passed in as a pointer to an integer. Why does it use
> array [nr >>5]?
Linux bitfields can have an arbitrary size, more than a single machine
word. Bitfields consist of a arrays of unsigned longs - note that this
makes a difference for 32-bit and 64-bit kernels!.
Ralf
