Re: [Patch] xfs_lowbit64 broken on ia32

[Lachlan McIlroy <lachlan@sgi.com>]

David Chinner wrote:
> The recent change to the internals of xfs_lowbit64 broke it on
> ia32 - the code treats the 64bit value as an unsigned long
> which is only 32 bits on ia32 and hence throws away the high 32
> bits. 64 bit platforms are not affected.
> 
> Tested with a userspace implementation comparing the original
> code with the new code.
> 
> Signed-off-by: Dave Chinner <dgc@sgi.com>
> ---
>  fs/xfs/xfs_bit.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: 2.6.x-xfs-new/fs/xfs/xfs_bit.h
> ===================================================================
> --- 2.6.x-xfs-new.orig/fs/xfs/xfs_bit.h	2007-11-02 13:44:45.000000000 +1100
> +++ 2.6.x-xfs-new/fs/xfs/xfs_bit.h	2007-12-03 14:43:33.169851481 +1100
> @@ -68,8 +68,8 @@ static inline int xfs_lowbit32(__uint32_
>  /* Get low bit set out of 64-bit argument, -1 if none set */
>  static inline int xfs_lowbit64(__uint64_t v)
>  {
> -	unsigned long	t = v;
> -	return (v) ? find_first_bit(&t, 64) : -1;
> +	unsigned long long	t = v;
Why create a local copy?  Why not just pass v into find_first_bit()?

> +	return (v) ? find_first_bit((unsigned long *)&t, 64) : -1;
>  }
>  
>  /* Return whether bitmap is empty (1 == empty) */
> 
> 
>