linux-kernel - Re: [PATCH 1/3] bitops: Add _

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Message-ID: <52615.1240839635@turing-police.cc.vt.edu>
Date:	Mon, 27 Apr 2009 09:40:35 -0400
From:	Valdis.Kletnieks@...edu
To:	Steven Whitehouse <swhiteho@...hat.com>
Cc:	linux-kernel@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: [PATCH 1/3] bitops: Add __ffs64 bitop

On Thu, 23 Apr 2009 10:16:54 BST, Steven Whitehouse said:
> Finds the first set bit in a 64 bit word. This is required in order
> to fix a bug in GFS2, but I think it should be a generic function
> in case of future users.

Seems like a sane idea..

> +static inline unsigned long __ffs64(u64 word)
> +{
> +#if BITS_PER_LONG == 32
> +	if (((u32)word) == 0UL)
> +		return __ffs((u32)(word >> 32)) + 32;
> +#elif BITS_PER_LONG != 64
> +#error BITS_PER_LONG not 32 or 64
> +#endif
> +	return __ffs((unsigned long)word);
> +}
> +

Does this have endian-ness issues (is that (u32)word the "high" or "low"
part)?  Or is this intended only for looking at bitmaps and the like, and we
don't really care?

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