From: Sean Young <sean@mess.org>
To: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
linux-media@vger.kernel.org
Subject: Re: [PATCH] media: rc: reduce size of struct ir_raw_event
Date: Thu, 17 Mar 2016 10:53:40 +0000 [thread overview]
Message-ID: <20160317105340.GA10247@gofer.mess.org> (raw)
In-Reply-To: <56EA517B.5030903@gmail.com>
On Thu, Mar 17, 2016 at 07:40:59AM +0100, Heiner Kallweit wrote:
> Am 16.03.2016 um 23:28 schrieb Sean Young:
> > On Wed, Mar 16, 2016 at 10:18:38PM +0100, Heiner Kallweit wrote:
> >> + u8 pulse:1;
> >> + u8 reset:1;
> >> + u8 timeout:1;
> >> + u8 carrier_report:1;
> >
> > Why are you changing the type of the bitfields?
> >
> I did this to make sure that the compiler uses one byte for
> the bit field. When testing gcc also used just one byte when
> keeping the original "unsigned" type for the bit field members.
> Therefore it wouldn't be strictly neeeded.
>
> But I'm not sure whether it's guaranteed that the compiler packs a
> bit field to the smallest possible data type and we can rely on it.
> AFAIK C99 is a little more specific about this implementation detail of
> bit fields but C89/C90 is used for kernel compilation.
It might be worth reading about structure packing rules rather than
guessing.
Sean
next prev parent reply other threads:[~2016-03-17 10:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-16 21:18 [PATCH] media: rc: reduce size of struct ir_raw_event Heiner Kallweit
2016-03-16 22:28 ` Sean Young
2016-03-17 6:40 ` Heiner Kallweit
2016-03-17 10:53 ` Sean Young [this message]
2016-03-17 19:37 ` Heiner Kallweit
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