Re: [PATCH v4 2/4] lib: vsprintf: Fix handling of number field widths in vsscanf

[Andy Shevchenko]

On Fri, Feb 5, 2021 at 5:23 PM David Laight <David.Laight@xxxxxxxxxx> wrote:
> From: Andy Shevchenko
> > Sent: 05 February 2021 12:51
> > On Fri, Feb 5, 2021 at 1:35 PM Richard Fitzgerald
> > <rf@xxxxxxxxxxxxxxxxxxxxx> 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.

off-by-one to be precise.

> If 'max_chars' is known to be non-zero the do ... while (--max_chars);
> loop will probable generate better code.

What?! while (--x)  and while(x--) are equivalent.

> But there is no accounting for just how odd some decisions gcc
> makes are.

Why should we care about the compiler bugs here?

-- 
With Best Regards,
Andy Shevchenko