On Wed, 2017-10-11 at 16:31 +0300, Andy Shevchenko wrote:
> On Wed, Oct 11, 2017 at 10:29 AM, sakari.ailus@xxxxxxxxxxxxxxx
> <sakari.ailus@xxxxxxxxxxxxxxx> wrote:
> > On Wed, Oct 11, 2017 at 04:14:37AM +0000, Zhi, Yong wrote:
> > > > > +static unsigned int ipu3_css_scaler_get_exp(unsigned int
> > > > > counter,
> > > > > + unsigned int
> > > > > divider) {
> > > > > + unsigned int i = 0;
> > > > > +
> > > > > + while (counter <= divider / 2) {
> > > > > + divider /= 2;
> > > > > + i++;
> > > > > + }
> > > > > +
> > > > > + return i;
> > return (!counter || divider < counter) ?
> > 0 : fls(divider / counter) - 1;
>
> Extra division is here (I dunno if counter is always power of 2 but
> it
> doesn't matter for compiler).
>
> Basically above calculates how much bits we need to shift divider to
> get it less than counter.
>
> I would consider to use something from log2.h.
>
> Roughly like
>
> if (!counter || divider < counter)
> return 0;
> return order_base_2(divider) - order_base_2(counter);
The original loop is typical ran just couple of times, so I think
that fls or division are probably slower than the original loop.
Furthermore, these "optimizations" are also harder to read, so in
my opinion there's no advantage in using them.
- Tuukka
