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

Simon Glass
2013-04-17T20:59:48Z

Hi Albert,

On Wed, Apr 17, 2013 at 12:23 PM, Albert ARIBAUD
<albert.u.boot@aribaud.net> wrote:
> Hi Simon -- and sorry for the dupe.
>
> On Wed, 17 Apr 2013 11:28:07 -0700, Simon Glass <sjg@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 at 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.

Regards,
Simon

[and sorry for my dup]