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 14:47:03 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org,
        Noralf Trønnes <noralf@...nnes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        dri-devel@...ts.freedesktop.org, Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH v4 1/6] drm/format-helper: Add
 drm_fb_xrgb8888_to_gray8_line()

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'.

-- 
Ville Syrjälä
Intel