On Fri, Feb 11, 2022 at 02:05:56PM +0200, Jani Nikula wrote:
> On Fri, 11 Feb 2022, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > Am 11.02.22 um 12:12 schrieb Andy Shevchenko:
> >> On Fri, Feb 11, 2022 at 11:40:13AM +0100, Javier Martinez Canillas wrote:
> >>> On 2/11/22 11:28, Andy Shevchenko wrote:
> >>>> On Fri, Feb 11, 2022 at 10:19:22AM +0100, Javier Martinez Canillas wrote:
...
> >>>>> +static void drm_fb_xrgb8888_to_gray8_line(u8 *dst, const u32 *src, unsigned int pixels)
> >>>>> +{
> >>>>> + unsigned int x;
> >>>>> +
> >>>>> + for (x = 0; x < pixels; x++) {
> >>>>> + u8 r = (*src & 0x00ff0000) >> 16;
> >>>>> + u8 g = (*src & 0x0000ff00) >> 8;
> >>>>> + u8 b = *src & 0x000000ff;
> >>>>> +
> >>>>> + /* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */
> >>>>> + *dst++ = (3 * r + 6 * g + b) / 10;
> >>>>> + src++;
> >>>>> + }
> >>>>
> >>>> Can be done as
> >>>>
> >>>> while (pixels--) {
> >>>> ...
> >>>> }
> >>>>
> >>>> or
> >>>>
> >>>> do {
> >>>> ...
> >>>> } while (--pixels);
> >>>>
> >>>
> >>> I don't see why a while loop would be an improvement here TBH.
> >>
> >> Less letters to parse when reading the code.
> >
> > It's a simple refactoring of code that has worked well so far. Let's
> > leave it as-is for now.
>
> IMO *always* prefer a for loop over while or do-while.
>
> The for (i = 0; i < N; i++) is such a strong paradigm in C. You
> instantly know how many times you're going to loop, at a glance. Not so
> with with the alternatives, which should be used sparingly.
while () {} _is_ a paradigm, for-loop is syntax sugar on top of it.
> And yes, the do-while suggested above is buggy, and you actually need to
> stop and think to see why.
It depends if pixels can be 0 or not and if it's not, then does it contain last
or number.
The do {} while (--pixels); might be buggy iff pixels may be 0.
--
With Best Regards,
Andy Shevchenko
