On Sat, 30 Jan 2010 17:45:17 +0800
Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> This allows use of hweight_long() in BUILD_BUG_ON().
> Suggested by Jamie.
>
> CC: Jamie Lokier <jamie@xxxxxxxxxxxxx>
> CC: Roland Dreier <rdreier@xxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> include/linux/bitops.h | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> --- linux-mm.orig/include/linux/bitops.h 2009-07-20 20:10:19.000000000 +0800
> +++ linux-mm/include/linux/bitops.h 2010-01-30 17:41:15.000000000 +0800
> @@ -40,10 +40,14 @@ static __inline__ int get_count_order(un
> return order;
> }
>
> -static inline unsigned long hweight_long(unsigned long w)
> -{
> - return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
> -}
> +#define hweight_long(x) \
> +( \
> + __builtin_constant_p(x) ? \
> + __builtin_popcountl(x) : \
> + (sizeof(x) <= 4 ? \
> + hweight32(x) : \
> + hweight64(x)) \
> +)
>
> /**
> * rol32 - rotate a 32-bit value left
Peter's been mucking with a compile-time HWEIGHT(). An outdated
version of that is presently in linux-next.
(I wonder if it could have used __builtin_popcount)
(I wonder which gcc versions support __builtin_popcount)
Anyway, I suspect you should be using that rather than tweaking
hweight_long().
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