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Subject: Re: [PATCH] add slice by 8 algorithm to crc32.c
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To: "George Spelvin" <linux@horizon.com>
Cc: akpm@linux-foundation.org, fzago@systemfabricworks.com,
        linux-kernel@vger.kernel.org, rpearson@systemfabricworks.com
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From: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Date: Mon, 8 Aug 2011 13:11:14 +0200
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"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.