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Re: [PATCH 7/9] xen/bitops: Implement hweight64() in terms of hweightl()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 26 Aug 2024 13:55:01 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 26 Aug 2024 11:55:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 23.08.2024 01:06, Andrew Cooper wrote:
> ... and drop generic_hweight64().
>
> This is identical on all architectures except ARM32. Add one extra SELF_TEST
> to check that hweight64() works when the input is split in half.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one remark:
> --- a/xen/include/xen/bitops.h
> +++ b/xen/include/xen/bitops.h
> @@ -302,6 +302,14 @@ static always_inline __pure unsigned int
> hweightl(unsigned long x)
> #endif
> }
>
> +static always_inline __pure unsigned int hweight64(uint64_t x)
> +{
> + if ( BITS_PER_LONG == 64 )
> + return hweightl(x);
> + else
> + return hweightl(x >> 32) + hweightl(x);
This assume BITS_PER_LONG == 32, which of course is true right now, but
doesn't need to be in general. Better add an explicit cast to uint32_t
(or masking by 0xffffffffU)?
Jan
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