[U-Boot] [PATCH] crc32: Correct endianness of crc32 result

[Albert ARIBAUD]

Hi Simon,

On Wed, 17 Apr 2013 13:59:48 -0700, Simon Glass <sjg at chromium.org>
wrote:

> Hi Albert,
> 
> On Wed, Apr 17, 2013 at 12:23 PM, Albert ARIBAUD
> <albert.u.boot at aribaud.net> wrote:
> > Hi Simon -- and sorry for the dupe.
> >
> > On Wed, 17 Apr 2013 11:28:07 -0700, Simon Glass <sjg at chromium.org>
> > wrote:
> >
> >> I tried using:
> >>
> >> #ifdef USE_HOSTCC
> >>    crc = htobe32(crc);
> >> #else
> >>    crc = cpu_to_be32(crc);
> >> #endif
> >>    memcpy(output, &crc, sizeof(crc));
> >>
> >>
> >> This is one instruction (4 bytes, 16%) smaller, but I suspect quite a
> >> lot slower due to the overhead of a very small memcpy().
> >>
> >> 43e2c1d8: e28d1008 add r1, sp, #8
> >> 43e2c1dc: e3a02004 mov r2, #4
> >> 43e2c1e0: e6bf0f30 rev r0, r0
> >> 43e2c1e4: e5210004 str r0, [r1, #-4]!
> >> 43e2c1e8: e1a00004 mov r0, r4
> >> 43e2c1ec: eb001af7 bl 43e32dd0 <memcpy>
> >
> > How about replacing the memcpy with an explicit put_unaligned(),
> > similar to what was done in
> >
> > http://www.mail-archive.com/u-boot@lists.denx.de/msg109555.html
> >
> > with get_unaligned()? The code will be longer than above, but shorter
> > than the above plus the memcpy(), and faster too -- actually, I'm
> > surprised that the compiler does not unroll the memcpy() on its own,
> > considering the size argument is a constant.
> 
> Do you mean like this?
> 
> #ifdef USE_HOSTCC
>    crc = htobe32(crc);
>    memcpy(output, &crc, sizeof(crc));
> #else
>    crc = cpu_to_be32(crc);
>    put_unaligned(crc, (uint32_t *)output);
> #endif
> 
> This produces the same code as my original patch. If this is
> acceptable then I will do that, although it doesn't really seem any
> better.

Wolfgang may not like it any more than put_unaligned_be32() as it
builds upon it (and the disk patch could have used the be32 version as
well). Personally, I think we should allow and use these...

... and work on optimizing their implementation for ARM; we should be
able to reduce such put()s and get()s to a few instructions. And to
avoid any misunderstanding, yes, I volunteer for the optimizing work. :)

> Regards,
> Simon
> 
> [and sorry for my dup]

Actually I'm the culprit.

Amicalement,
-- 
Albert.