On Thu, Dec 03, 2020 at 03:27:33AM +0900, Yun Levi wrote:
> On Thu, Dec 3, 2020 at 2:36 AM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > On Wed, Dec 02, 2020 at 09:26:05AM -0800, Yury Norov wrote:
...
> > Side note: speaking of performance, any plans to fix for_each_*_bit*() for
> > cases when the nbits is known to be <= BITS_PER_LONG?
> >
> > Now it makes an awful code generation (something like few hundred bytes of
> > code).
> Frankly Speaking, I don't have an idea in now.....
> Could you share your idea or wisdom?
Something like (I may be mistaken by names, etc, I'm not a compiler expert,
and this is in pseudo language, I don't remember all API names by hart,
just to express the idea) as a rough first step
__builtin_constant(nbits, find_next_set_bit_long, find_next_set_bit)
find_next_set_bit_long()
{
unsigned long v = BIT_LAST_WORD(i);
return ffs_long(v);
}
Same for find_first_set_bit() -> map it to ffs_long().
And I believe it can be optimized more.
--
With Best Regards,
Andy Shevchenko
