From: Alexander Aring <alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public•gmane.org>
To: Joe Perches <joe-6d6DIl74uiNBDgjK7y7TUQ@public•gmane.org>
Cc: "netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org"
<netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org>,
"linux-zigbee-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public•gmane.org"
<linux-zigbee-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public•gmane.org>,
David Laight
<David.Laight-ZS65k/vG3HxXrIkS9f7CXA@public•gmane.org>,
"davem-fT/PcQaiUtIeIZ0/mPfg9Q@public•gmane.org"
<davem-fT/PcQaiUtIeIZ0/mPfg9Q@public•gmane.org>
Subject: Re: [PATCH net-next v4 2/8] 6lowpan: add uncompress header size function
Date: Wed, 26 Feb 2014 19:32:11 +0100 [thread overview]
Message-ID: <20140226183209.GA31268@omega> (raw)
In-Reply-To: <1393439085.407.31.camel@joe-AO722>
On Wed, Feb 26, 2014 at 10:24:45AM -0800, Joe Perches wrote:
> On Wed, 2014-02-26 at 16:10 +0000, David Laight wrote:
> > From: Alexander Aring
> []
> > > diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h
> []
> > > +static inline u8 lowpan_addr_mode_size(const u8 addr_mode)
> > > +{
> > > + switch (addr_mode) {
> > > + case LOWPAN_IPHC_ADDR_00:
> > > + return 16;
> > > + case LOWPAN_IPHC_ADDR_01:
> > > + return 8;
> > > + case LOWPAN_IPHC_ADDR_02:
> > > + return 2;
> > > + default:
> > > + return 0;
> > > + }
> > > +}
> >
> > The compiler will generate much better code if you index an array instead
> > of using a switch statement.
>
> Are you sure of that?
>
> Perhaps the compiler would inline the assignment
> anyway if addr_mode is __builtin_constant_p
>
> gcc 4.8 here does the same thing with:
>
> static inline unsigned char f1(unsigned char a)
> {
> switch (a) {
> case 0: return 16;
> case 1: return 8;
> case 2: return 2;
> default: return 0;
> }
> }
>
> static inline unsigned char f2(unsigned char a)
> {
> static const unsigned char rtns[] = { 16, 8, 2, 0 };
>
> return rtns[a & 3];
> }
to make a mask with & 3 is already done, so we don't need that.
I am not sure what I should do now, change or not change? :-)
- Alex
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next prev parent reply other threads:[~2014-02-26 18:32 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-26 16:05 [PATCH net-next v4 0/8] 6lowpan: reimplementation of fragmentation handling Alexander Aring
2014-02-26 16:05 ` [PATCH net-next v4 2/8] 6lowpan: add uncompress header size function Alexander Aring
2014-02-26 16:10 ` David Laight
2014-02-26 16:20 ` Alexander Aring
2014-02-26 17:05 ` David Laight
2014-02-26 18:24 ` Joe Perches
2014-02-26 18:32 ` Alexander Aring [this message]
2014-02-26 18:35 ` Joe Perches
2014-02-26 18:56 ` David Miller
2014-02-26 16:05 ` [PATCH net-next v4 3/8] 6lowpan: fix fragmentation on sending side Alexander Aring
2014-02-26 16:05 ` [PATCH net-next v4 5/8] 6lowpan: move 6lowpan.c to 6lowpan_rtnl.c Alexander Aring
[not found] ` <1393430712-11298-1-git-send-email-alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-02-26 16:05 ` [PATCH net-next v4 1/8] 6lowpan: add frag information struct Alexander Aring
2014-02-26 16:05 ` [PATCH net-next v4 4/8] 6lowpan: change tag type to __be16 Alexander Aring
2014-02-26 16:05 ` [PATCH net-next v4 6/8] 6lowpan: fix some checkpatch issues Alexander Aring
[not found] ` <1393430712-11298-7-git-send-email-alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-02-26 17:24 ` Joe Perches
2014-02-26 18:59 ` David Miller
2014-02-26 16:05 ` [PATCH net-next v4 7/8] net: ns: add ieee802154_6lowpan namespace Alexander Aring
2014-02-26 16:05 ` [PATCH net-next v4 8/8] 6lowpan: handling 6lowpan fragmentation via inet_frag api Alexander Aring
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