linux-kernel - RE: [PATCH v4 2/4] lib: vsprintf: Fix handling of number field widths in vsscanf

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Message-ID: <82696a371fe447c2b201fc812e5a4560@AcuMS.aculab.com>
Date:   Fri, 5 Feb 2021 15:23:46 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andy Shevchenko' <andy.shevchenko@...il.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
CC:     Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Shuah Khan <shuah@...nel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "patches@...nsource.cirrus.com" <patches@...nsource.cirrus.com>
Subject: RE: [PATCH v4 2/4] lib: vsprintf: Fix handling of number field widths
 in vsscanf

From: Andy Shevchenko
> Sent: 05 February 2021 12:51
> 
> On Fri, Feb 5, 2021 at 1:35 PM Richard Fitzgerald
> <rf@...nsource.cirrus.com> wrote:
> > On 04/02/2021 16:35, Petr Mladek wrote:
> > > On Wed 2021-02-03 21:45:55, Andy Shevchenko wrote:
> > >> On Wed, Feb 03, 2021 at 04:50:07PM +0000, Richard Fitzgerald wrote:
> 
> ...
> 
> > >>> +   for (; max_chars > 0; max_chars--) {
> > >>
> > >> Less fragile is to write
> > >>
> > >>      while (max_chars--)
> > >
> > > Except that the original was more obvious at least for me.
> > > I always prefer more readable code when the compiler might do
> > > the optimization easily. But this is my personal taste.
> > > I am fine with both variants.
> 
> I *slightly* prefer while-loop *in this case* due to less characters
> to parse to understand the logic.

The two loops are also have different values for 'max_chars'
inside the loop body.

If 'max_chars' is known to be non-zero the do ... while (--max_chars);
loop will probable generate better code.
But there is no accounting for just how odd some decisions gcc
makes are.

	David

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