Re: [PATCH] add slice by 8 algorithm to crc32.c

[Joakim Tjernlund]

"George Spelvin" <linux@xxxxxxxxxxx> 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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/