Re: union/struct representations for MAS Registers

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

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quoted

quoted

Bitfields are rather non-portable, the compiler has a lot of choice
about how to align the bits in memory.

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I'm ok with the masking stuff.
However, I'm actually surprised this is true given the=20
maturity of our ABIs.

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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.
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Different architectures can (and do) assign things in different ways.
So code that is ok on ppc might fail on arm or x86 (etc).
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	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=