linux-kernel - RE: [PATCH] add slice by 8 algorithm to crc32.c

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Date:	Mon, 8 Aug 2011 11:54:34 -0500
From:	"Bob Pearson" <rpearson@...temfabricworks.com>
To:	"'George Spelvin'" <linux@...izon.com>,
	<joakim.tjernlund@...nsmode.se>
Cc:	<akpm@...ux-foundation.org>, <fzago@...temfabricworks.com>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] add slice by 8 algorithm to crc32.c



> -----Original Message-----
> From: George Spelvin [mailto:linux@...izon.com]
> Sent: Monday, August 08, 2011 5:52 AM
> To: joakim.tjernlund@...nsmode.se; linux@...izon.com
> Cc: akpm@...ux-foundation.org; fzago@...temfabricworks.com; linux-
> kernel@...r.kernel.org; rpearson@...temfabricworks.com
> Subject: Re: [PATCH] add slice by 8 algorithm to crc32.c
> 
> > I prefer to keep the current code which (at the time) generated good
code
> > for at least ppc:
> > 	/* Align it */
> > 	if (unlikely((long)buf & 3 && len)) {
> > 		do {
> > 			DO_CRC(*buf++);
> > 		} while ((--len) && ((long)buf)&3);
> > 	}
> 
> Ah, I was looking at fzago's initial patch; I hadn't realized you'd
> tweaked it.  That's pretty much what I was talking about.

Frank actually deserves none of the 'blame' for this effort. He is much more
experienced in sending in patches to linux-kernel than I am and helped me to
prepare and send the first version of the patch.

> 
> Would
>  	if (unlikely((long)buf & 3) && len) {
> 
> give the compiler better hints?  len != 0 is awfully
> likely, actually.

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