Re: union/struct representations for MAS Registers

[Kumar Gala <galak@kernel.crashing.org>]

On Aug 10, 2011, at 12:38 PM, David Laight wrote:

>=20
>>> Bitfields are rather non-portable, the compiler has a lot of choice
>>> about how to align the bits in memory.
>>=20
>> I'm ok with the masking stuff.
>> However, I'm actually surprised this is true given the=20
>> maturity of our ABIs.
>=20
> The C standard says nothing at all about how bitfields are =
implemented,
> I think the first bit might be 0x1, 0x80, 0x1000000 or 0x80000000
> when treated as a 32bit value, regardless of the endianness.
>=20
> Different architectures can (and do) assign things in different ways.
> So code that is ok on ppc might fail on arm or x86 (etc).
>=20
> 	David

I think PPCs a bit sane and what Jimi was proposing the union for is =
something that would never need to be portable (as it a PPC specific =
register).

Still, prefer the shifts, masks & macros as that's what I've been =
reading & using in ppc land forever ;)

- k=