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Subject: Re: [Qemu-devel] [PATCH v1 4/8] target-ppc: add vabsdu[b, h,
 w] instructions
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To: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>, qemu-ppc@nongnu.org, david@gibson.dropbear.id.au
Cc: qemu-devel@nongnu.org, bharata@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, benh@kernel.crashing.org, Sandipan Das <sandipandas1990@gmail.com>

On 07/28/2016 12:19 PM, Nikunj A Dadhania wrote:
> +        r->element[i] = abs(a->element[i] - b->element[i]);             \
> +    }                                                                   \
> +}
> +
> +/* VABSDU - Vector absolute difference unsigned
> + *   name    - instruction mnemonic suffix (b: byte, h: halfword, w: word)
> + *   element - element type to access from vector
> + */
> +#define VABSDU(type, element)                   \
> +    VABSDU_DO(absdu##type, element)
> +VABSDU(b, u8)
> +VABSDU(h, u16)
> +VABSDU(w, u32)

 From whence are you receiving this abs definition, and how do you expect it to 
work with an unsigned input?

I can only imagine you're getting abs(3), aka int abs(int), from stdlib.h. 
Which technically does work post-arithmetic promotion for u8 and u16, but it 
does not for u32.

I think we'd prefer an explicit (a > b ? a - b : b - a).


r~