On Fri, 11 Feb 2022, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> Hi
>
> 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.
And yes, the do-while suggested above is buggy, and you actually need to
stop and think to see why.
BR,
Jani.
>
> Best regards
> Thomas
>
>>
>>> In any case, I just pulled the line conversion logic as a separate
>>> function with minimal code changes since doing that should be in a
>>> separate patch.
>>
>>
>>> Feel free to post a patch if you want to change that while loop.
>>
>> Perhaps some day :-)
>>
--
Jani Nikula, Intel Open Source Graphics Center
