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From: "Bob Pearson" <rpearson@systemfabricworks.com>
To: "'Joakim Tjernlund'" <joakim.tjernlund@transmode.se>,
        "'George Spelvin'" <linux@horizon.com>
Cc: <akpm@linux-foundation.org>, <fzago@systemfabricworks.com>,
        <linux-kernel@vger.kernel.org>
References: <OF53580ACE.F420CB68-ONC12578E6.0039189A-C12578E6.0039CD0F@transmode.se> <20110808105201.25396.qmail@science.horizon.com> <OFEA1BD2B2.B2A7F07F-ONC12578E6.003D368C-C12578E6.003D7468@transmode.se>
In-Reply-To: <OFEA1BD2B2.B2A7F07F-ONC12578E6.003D368C-C12578E6.003D7468@transmode.se>
Subject: RE: [PATCH] add slice by 8 algorithm to crc32.c
Date: Mon, 8 Aug 2011 12:04:05 -0500
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Same for x86. The code for the pre and post cleanup loops are the same
there.

> -----Original Message-----
> From: Joakim Tjernlund [mailto:joakim.tjernlund@transmode.se]
> Sent: Monday, August 08, 2011 6:11 AM
> To: George Spelvin
> Cc: akpm@linux-foundation.org; fzago@systemfabricworks.com; linux-
> kernel@vger.kernel.org; rpearson@systemfabricworks.com
> Subject: Re: [PATCH] add slice by 8 algorithm to crc32.c
> 
> "George Spelvin" <linux@horizon.com> wrote on 2011/08/08 12:52:01:
> >
> > > 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.
> >
> > Would
> >     if (unlikely((long)buf & 3) && len) {
> >
> > give the compiler better hints?  len != 0 is awfully
> > likely, actually.
> 
> Doesn't matter on ppc(gcc 4.4.4). The whole while loop is moved out of
line
> in both cases and the generated asm is identical.