On Wed, 15 Jul 2026 at 02:18, Pierrick Bouvier
<[email protected]> wrote:
>
> On 7/14/2026 8:51 AM, Brian Cain wrote:
> > set_bit32()/test_bit32()/etc already let devices operate on
> > guest-visible uint32_t register arrays without depending on the
> > host's 'unsigned long' size. find_first_bit() has no such
> > equivalent, which pushes callers towards casting a uint32_t array
> > to 'unsigned long *'.
> >
> > Add find_first_bit32(), implemented the same way as find_first_bit().
> >
> > Signed-off-by: Brian Cain <[email protected]>
> > +/**
> > + * find_first_bit32 - find the first set bit in a memory region
> > + * @addr: The address to start the search at
> > + * @size: The maximum size to search
> > + *
> > + * Returns the bit number of the first set bit,
> > + * or @size if there is no set bit in the bitmap.
> > + */
> > +static inline uint32_t find_first_bit32(const uint32_t *addr, uint32_t
> > size)
> > +{
> > + uint32_t result;
> > +
> > + for (result = 0; result < size; result += 32) {
> > + uint32_t tmp = *addr++;
> > + if (tmp) {
> > + result += ctz32(tmp);
> > + return result < size ? result : size;
> > + }
> > + }
> > + /* Not found */
> > + return size;
> > +}
>
> Either we should express size in terms of number of elements, or add an
> explicit check if size is not a multiple of 32.
I think we should follow the API of the existing find_first_bit()
function here, which defines the size in terms of number of bits.
Sizes not a multiple of 32 should work fine -- the representation
is "bit 0 in LSB of first 32 bit word, working upwards". So e.g.
an bitmap of 16 bits has the representation "a single 32 bit word,
and the bits are in bits 0..15". The code correctly handles this
with the "return result < size ? result : size" logic: even if
bit 17 is set, we will return 16 to indicate "no set bit in bitmap".
(This also follows the existing find_first_bit() handling.)
thanks
-- PMM
