From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751947AbeB0FTL (ORCPT ); Tue, 27 Feb 2018 00:19:11 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:40939 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751037AbeB0FTK (ORCPT ); Tue, 27 Feb 2018 00:19:10 -0500 Date: Tue, 27 Feb 2018 06:19:05 +0100 From: Willy Tarreau To: Robert Abel Cc: Miguel Ojeda , linux-kernel , Geert Uytterhoeven , Andy Shevchenko Subject: Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands Message-ID: <20180227051905.GA26781@1wt.eu> References: <9ec3c54c-f8fe-22d7-783e-8cf9862405bb@robertabel.eu> <20180225235432.31209-1-rabel@robertabel.eu> <20180225235432.31209-2-rabel@robertabel.eu> <20180225235432.31209-3-rabel@robertabel.eu> <20180225235432.31209-4-rabel@robertabel.eu> <50a2fd51-8bdb-d2b7-c2b3-7df638fdedde@robertabel.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50a2fd51-8bdb-d2b7-c2b3-7df638fdedde@robertabel.eu> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 26, 2018 at 11:43:36PM +0100, Robert Abel wrote: > On 26 Feb 2018 17:49, Miguel Ojeda wrote: > > On a general note, the code seems a bit convoluted for what it does, > > specially without the comment written in the commit message :-) Isn't > > it simpler to use a tiny array in the stack and put the numbers to be > > converted instead of modifying the input sequence and dancing with > > pointers? > > That's what I felt at first, too. If we can drop the backwards > compatibility of repeated xy commands, the whole affair gets much > easier, but will unfortunately break existing use. > > Ex. ^[[Lx004y002x006; --> x6y2, because repeats of x would just > overwrite earlier values. That's what the while loop allowed in the > first place. > > I suspect the while loop to parse was just a clever way of parsing y > followed by x and x followed by y using the same code and the > overwriting behavior is actually an unaccounted-for side-effect. Well actually I don't see a problem there at all. The principle is simply to accept any sequence assigning x or y or both. If you write x4y2x6, it simply means that you changed your mind regarding x and that the last value (6) is the one you want. Just as if you wrote "^[[Lx4;^[[y2;^[[x6;". The while loop doesn't even try to do anything clever, it simply parses everything matching x and y followed by digits. I think the only reason for having both x and y processed in the same loop was to call charlcd_gotoxy() only once for both axes. Regards, Willy