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

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Message-ID: <YgoxFBGNsrezVxmi@smile.fi.intel.com>
Date:   Mon, 14 Feb 2022 12:38:12 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        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()

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:

	The for statement ... is equivalent to ... while..."

They said that for is equivalent to while, and not otherwise.

Also, syntax sugar by definition declares something that can be written as
a single line of code, which usually is done using more (not always).

> 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.

> > > 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