Re: [PATCH 1/2] Fix sign extension of bitmap_offset in super1.c

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 04/26/12 17:32, Richard Henderson wrote:
> On 04/26/12 08:25, Jes Sorensen wrote:
>> Just checking mdadm.h and bswap32() is defined like this:
>>
>> #define bswap_32(x) (((x) & 0x000000ffU) << 24 | \
>>                      ((x) & 0xff000000U) >> 24 | \
>>                      ((x) & 0x0000ff00U) << 8  | \
>>                      ((x) & 0x00ff0000U) >> 8)
>>
>> so I am not 100% sure just swapping to an s32 in the struct will work on
>> big endian systems? Will the 0x000000ffU not force the conversion back
>> to unsigned or what happens in this case?
> 
> This is actually semi-complicated.  c89 or c99 rules?  X already of a
> type larger than unsigned int?

This is what I was afraid of :)

> But if X is signed int, this entire expression will always be unsigned.
> 
> You're certainly better off with a cast as we discussed on irc.

In this particular case X would be a signed int, so we would end up with
unsigned and still need the cast.

I will opt for the cast in this case - thanks a lot for the clarification.

Cheers,
Jes