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 11:57:20 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        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>,
        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 Andy,

On Mon, Feb 14, 2022 at 11:39 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> 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.

When I learned C, people told me to prefer while() over for() when
possible, as several compilers are better at optimizing while()-loops
than for()-loops.

During the last 3 decades, optimizers got better, and all the bad
old compilers went the way of the dodo (see also [1])...
But even for a human, it's still less symbols to decode (and verify
all the details about =/</>/<=/>=/++/--/...) for

    while (n--) { ... }

than for

   for (i = 0; i < n; i++) { ... }

[1] https://lwn.net/Articles/871283/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds