On Fri, Feb 11, 2022 at 06:25:17PM +0200, Jani Nikula wrote:
On Fri, 11 Feb 2022, Andy Shevchenko andriy.shevchenko@linux.intel.com wrote:
On Fri, Feb 11, 2022 at 02:05:56PM +0200, Jani Nikula wrote:
On Fri, 11 Feb 2022, Thomas Zimmermann tzimmermann@suse.de 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 while() is just syntax sugar for goto. :p
The for loop written as for (i = 0; i < N; i++) is hands down the most obvious counting loop pattern there is in C.
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.
Yeah. And how long does it take to figure that out?
Okay, I made a mistake to drop the explanation. So, I (mistakenly) assumed that people know this difference between post-decrement and pre-decrement (note, while-loop here is not what is problematic).