linux-kernel - Re: [PATCH v4 1/6] drm/format-helper: Add drm_fb_xrgb8888_to_gray8

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Date:   Mon, 14 Feb 2022 13:54:59 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Javier Martinez Canillas <javierm@...hat.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v4 1/6] drm/format-helper: Add
 drm_fb_xrgb8888_to_gray8_line()

Hi

Am 14.02.22 um 13:47 schrieb Ville Syrjälä:
> On Mon, Feb 14, 2022 at 01:12:48PM +0100, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 14.02.22 um 11:38 schrieb Andy Shevchenko:
>>> On Mon, Feb 14, 2022 at 10:03:53AM +0100, Thomas Zimmermann wrote:
>>>> Am 11.02.22 um 16:41 schrieb Andy Shevchenko:
>>>
>>> ...
>>>
>>>>>> 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.
>>>>
>>>> Naw, that's not true.
>>>
>>> In the section 3.5 "Loops - While and For" in "The C Programming
>>> Language" 2nd by K&R, the authors said:
>>
>> Year of publication: 1988 . It's not the most up-to-date reference for C
>> programming.
>>
>>>
>>> 	The for statement ... is equivalent to ... while..."
>>>
>>> They said that for is equivalent to while, and not otherwise.
>>
>> Even leaving readability aside, it's not equivalent. You can declare
>> variables as part of the for statement. (I know it's not the kernel's
>> style.) Also, 'continue' statements are not well-suited in for loops,
>> because it's non-obvious if the loop's update statement is being
>> executed. (It isn't.)
> 
> It is.
> 
> 'continue' is just shorthand for 'goto end_of_loop_body'.

Well, indeed. lol

Fun fact: I actually had to look this up and still got it wrong. Let me 
just count it under proving-my-point: continue in a for statement is a 
bad idea and for isn't equivalent to while.

Best regards
Thomas

> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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