Re: [PATCH 19/22] bbu: Remove logical negation in barebox_update_handler_exists()

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Barebox List <barebox@lists.infradead.org>
Subject: Re: [PATCH 19/22] bbu: Remove logical negation in barebox_update_handler_exists()
Date: Thu, 23 Aug 2018 08:42:45 +0200	[thread overview]
Message-ID: <20180823064245.hkxboqum2qxilifg@pengutronix.de> (raw)
In-Reply-To: <CAHQ1cqHr=a5CJrZ_ZhDUGxNu3Z48SVN4d30isVV4XVLZC1vy_g@mail.gmail.com>

On Wed, Aug 22, 2018 at 05:01:41PM -0700, Andrey Smirnov wrote:
> On Wed, Aug 22, 2018 at 12:09 AM Sascha Hauer <s.hauer@pengutronix.de> wrote:
> >
> > On Mon, Aug 20, 2018 at 11:26:00PM -0700, Andrey Smirnov wrote:
> > > Returning !bbu_find_handler() from barebox_update_handler_exists()
> > > would return the opposite result from what the name of that funciton
> > > implies. Drop the "!" to make it behave as expected.
> > >
> > > Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> > > ---
> > >  common/bbu.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/common/bbu.c b/common/bbu.c
> > > index 11e44f4a7..69ccac68a 100644
> > > --- a/common/bbu.c
> > > +++ b/common/bbu.c
> > > @@ -151,7 +151,7 @@ bool barebox_update_handler_exists(struct bbu_data *data)
> > >       if (!data->handler_name)
> > >               return false;
> > >
> > > -     return !bbu_find_handler(data->handler_name);
> > > +     return bbu_find_handler(data->handler_name);
> >
> > As bbu_find_handler() returns a pointer maybe better '!!' or
> > bbu_find_handler() != NULL?
> >
> 
> That shouldn't be necessary since barebox_update_handler_exists()
> returns bool(real type name is _Bool) which explicitly specifies that
> a cast of any scalar value to it would be normalized to 1 or 0 (as per
> C99 standard from whence it came). Otherwise you'd be able to end up
> in a situation where bool1 && bool2 && (bool1 != bool2) evaluates to
> true.
> 
> To give you more concrete example, here's what the last portion of
> that function compiles to on AArch64:
> 
>     2924: 97ffff5e     bl 269c <bbu_find_handler>
>     2928: f100001f   cmp x0, #0x0
>     292c: 1a9f07e0  cset w0, ne  // ne = any
>     2930: f9400bf3   ldr x19, [sp, #16]
>     2934: a8c27bfd  ldp x29, x30, [sp], #32
>     2938: d65f03c0  ret
>     293c: 52800020 mov w0, #0x1                    // #1
>     2940: 17fffffc      b 2930 <barebox_update_handler_exists+0x30>
>     2944: 52800000 mov w0, #0x0                    // #0
>     2948: 17fffffa      b 2930 <barebox_update_handler_exists+0x30>
> 
> and on AArch32 (Thumb):
> 
>     18e0: f7ff ff48 bl 1774 <bbu_find_handler>
>     18e4: 3000     adds r0, #0
>     18e6: bf18      it ne
>     18e8: 2001     movne r0, #1
>     18ea: bd10     pop {r4, pc}
>     18ec: 2001     movs r0, #1
>     18ee: e7fc      b.n 18ea <barebox_update_handler_exists+0x1a>
> 
> as you can see both cases already have code to explicitly convert the
> result of the function to 0/1.
> 
> I am more than happy to add ether !! or != NULL if you still think
> that'd be better, it just I don't think it will have any practical
> effect.

For sure it doesn't have a practical effect, it's merely a sign to show
"I know I'm casting a pointer to bool". Probably I'm just used to add
an explicit cast there and it's just a matter of taste.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

_______________________________________________
barebox mailing list
barebox@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/barebox