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From: Richard Henderson <rth@twiddle.net>
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Date: Thu, 24 Nov 2016 09:14:46 +0100
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Subject: Re: [Qemu-devel] [PATCH v1 09/10] target-ppc: add vextu[bhw]lx
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To: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>, David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, bharata@linux.vnet.ibm.com, Avinesh Kumar <avinesku@linux.vnet.ibm.com>

On 11/24/2016 06:53 AM, Nikunj A Dadhania wrote:
> David Gibson <david@gibson.dropbear.id.au> writes:
>
>> [ Unknown signature status ]
>> On Wed, Nov 23, 2016 at 05:07:18PM +0530, Nikunj A Dadhania wrote:
>>> From: Avinesh Kumar <avinesku@linux.vnet.ibm.com>
>>>
>>> vextublx:  Vector Extract Unsigned Byte Left
>>> vextuhlx:  Vector Extract Unsigned Halfword Left
>>> vextuwlx:  Vector Extract Unsigned Word Left
>>>
>>> Signed-off-by: Avinesh Kumar <avinesku@linux.vnet.ibm.com>
>>> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
>>
>> So, when I suggested doing these without helpers before, I had
>> forgotten that the non-byte versions can straddle the word boundary.
>> Given that the offset is in a register, not the instruction that does
>> make it complicated.
>>
>> But, this version also relies on working 128-bit arithmetic, AFAICT
>> this will just fail to build if CONFIG_INT128 isn't defined.
>
> It has both the implementation, just that the defines might have
> confused you:
>
> #if defined(HOST_WORDS_BIGENDIAN)
>
> #  if defined(CONFIG_INT128)
> #  else
> #  endif
>
> #else /* !defined (HOST_WORDS_BIGENDIAN) */
>
> #  if defined(CONFIG_INT128)
> #  else
> #  endif
>
> #endif

In include/qemu/int128.h, we do have int128_rshift.  So you don't *really* have 
to do this by hand, exactly.


r~