netdev - Re: [PATCH net-next v4 2/8] 6lowpan: add uncompress header size function

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Date:	Wed, 26 Feb 2014 17:20:10 +0100
From:	Alexander Aring <alex.aring@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"alex.bluesman.smirnov@...il.com" <alex.bluesman.smirnov@...il.com>,
	"dbaryshkov@...il.com" <dbaryshkov@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-zigbee-devel@...ts.sourceforge.net" 
	<linux-zigbee-devel@...ts.sourceforge.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"martin.townsend@...lon.com" <martin.townsend@...lon.com>
Subject: Re: [PATCH net-next v4 2/8] 6lowpan: add uncompress header size
 function

Hi David,

thanks for your reply.

On Wed, Feb 26, 2014 at 04:10:05PM +0000, David Laight wrote:
> From: Alexander Aring
> > Signed-off-by: Alexander Aring <alex.aring@...il.com>
> > ---
> >  net/ieee802154/6lowpan.h | 116 +++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 116 insertions(+)
> > 
> > diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h
> > index 2b835db..b6ae0bc 100644
> > --- a/net/ieee802154/6lowpan.h
> > +++ b/net/ieee802154/6lowpan.h
> > @@ -306,6 +306,122 @@ static inline void lowpan_push_hc_data(u8 **hc_ptr, const void *data,
> >  	*hc_ptr += len;
> >  }
> > 
> > +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.
> 
> 

You mean something like:

static inline u8 lowpan_addr_mode_size(const u8 addr_mode)
{
        const u8 res[] = { 16, 8, 2, 0 };
        return res[addr_mode];
}

or should I drop the array from the stack and declare it static?

?

- Alex
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