netdev - Re: [PATCH] bluetooth.h: __ variants of u8 and friends are not neccessary inside kernel

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Message-ID: <20161006070237.GB25972@amd>
Date:   Thu, 6 Oct 2016 09:02:38 +0200
From:   Pavel Machek <pavel@....cz>
To:     Joe Perches <joe@...ches.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bluetooth.h: __ variants of u8 and friends are not
 neccessary inside kernel

On Wed 2016-10-05 15:28:51, Joe Perches wrote:
> On Thu, 2016-10-06 at 00:13 +0200, Pavel Machek wrote:
> > On Wed 2016-10-05 12:15:34, Joe Perches wrote:
> > > On Wed, 2016-10-05 at 21:11 +0200, Pavel Machek wrote:
> > > > On Wed 2016-10-05 10:53:16, Joe Perches wrote:
> []
> > > > > trivia:
> > > > > It's generally faster to use bool instead of u8 foo:1;
> > > > Ok, but I'm not changing that in this patch.
> > > > (And actually, bool will take a lot more memory, right?)
> > > No worries, and bool is the same size as u8.
> > Exactly what I'm talking about :-). One byte vs. one bit, right?
> 
> Memory isn't bit addressable.
> So it's the same byte, it just doesn't use a read/modify/write
> operation to update a value.

I believe you are wrong. bit addressability does not matter, cpu can
definitely get the bit values.

u8 foo:1;
u8 bar:1;
u8 baz:1;

should take 1 byte, where

bool foo, bar, baz;

will take more like 3.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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