Re: [PATCH v2] net: ppp: use {get,put}_unaligned_be{16,32}

[Eric Dumazet <eric.dumazet@gmail.com>]

Le samedi 08 janvier 2011 à 11:04 +0100, Jarek Poplawski a écrit :

> Just for the record: I agree with Paul that current code is more readable.
> This code still requires thinking about specific bytes and the patch mixes
> it only with word access.
> 
> Jarek P.
> 
> > @@ -395,16 +396,14 @@ mppe_compress(void *arg, unsigned char *ibuf, unsigned char *obuf,
> >  	 */
> >  	obuf[0] = PPP_ADDRESS(ibuf);
> >  	obuf[1] = PPP_CONTROL(ibuf);
> > -	obuf[2] = PPP_COMP >> 8;	/* isize + MPPE_OVHD + 1 */
> > -	obuf[3] = PPP_COMP;	/* isize + MPPE_OVHD + 2 */
> > +	put_unaligned_be16(PPP_COMP, obuf + 2);
> >  	obuf += PPP_HDRLEN;

Compilers are stupid not generating optimal code, so we should help them
a bit.

Yes, I agree this is ugly Jarek and makes reading of this code a bit
more complex, but this is a move we cannot stop. Number of functions,
macros, etc... is exploding and we must follow the trend ;)

41 c6 44 24 02 00       movb   $0x0,0x2(%r12)
41 c6 44 24 03 fd       movb   $0xfd,0x3(%r12)

After patch :

66 41 c7 44 24 02 00 fd   movw   $0xfd00,0x2(%r12)