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 10:03:53 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v4 1/6] drm/format-helper: Add
 drm_fb_xrgb8888_to_gray8_line()

Hi

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. An idiomatic for loop, such as for (i = ...; i < 
N; ++i), is such a strong pattern that it's way better than the 
corresponding while loop.

Best regards
Thomas

> 
>> 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.
> 

-- 
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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