linux-kernel - Re: [PATCH v2] leds: ledtrig-morse: send out morse code

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Message-ID: <CAMuHMdUKpF=x-Se=9sKqiaWCr3YqPH1XOxK-sR=gvQ8uZBOnbg@mail.gmail.com>
Date:   Wed, 4 Jul 2018 09:46:53 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Willy Tarreau <w@....eu>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Andreas Klinger <ak@...klinger.de>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>,
        Ben Whitten <ben.whitten@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH v2] leds: ledtrig-morse: send out morse code

Hi Willy,

On Wed, Jul 4, 2018 at 4:41 AM Willy Tarreau <w@....eu> wrote:
> On Tue, Jul 03, 2018 at 09:43:06PM +0300, Andy Shevchenko wrote:
> > > +       {'a', ".-"},
> > > +       {'b', "-..."},

> >
> > Do you expect this to be changed somehow?
> > Otherwise we might just to keep two char arrays of alphas and digits
> > in an order of ascii appearance.
> >
> > In the code something like
> >
> > ch = tolower(x);
> > if (isalpha(ch))
> >  code = alphas[ch - 'a'];
> > else if (isdigit(ch))
> >  code = digits[ch - '0'];
> > else
> >  code = unknown;
> >
> > > +       {0, NULL},
> >
> > And this will gone, you just provide it with known size,
>
> Well, in this case it's even possible to go further and avoid storing
> 36 strings. Indeed, no representation is longer than 5 symbols, so you
> can use 5 bits for the encoding (0=".", 1="-") and 3 bits for the
> length, it gives you a single byte per character instead of a pointer
> to a string plus 6 chars. Then in order to make it readable, 5 macros

Hehe, https://lkml.org/lkml/2018/6/28/544 ;-)

> can be provided to emit the code :
>
> #define MORSE1(a,b)       (1 | ((a)<<3))
> #define MORSE2(a,b)       (2 | ((a)<<3)|((b)<<4))
> #define MORSE3(a,b,c)     (3 | ((a)<<3)|((b)<<4)|((c)<<5))
> #define MORSE4(a,b,c,d)   (4 | ((a)<<3)|((b)<<4)|((c)<<5)|((d)<<6))
> #define MORSE5(a,b,c,d,e) (5 | ((a)<<3)|((b)<<4)|((c)<<5)|((d)<<6)|((e)<<7))
>
> Then all chars may be defined like this :
>
>     ['a'] = MORSE2(0,1),
>     ['b'] = MORSE4(1,0,0,0),
>     ['c'] = MORSE4(1,0,1,0),
>     ['d'] = MORSE3(1,0,0),
>     ['e'] = MORSE1(0),

Nice!

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