Re: [RFC] __ffs64()

From: Christoph Lameter
Date: Wed Apr 22 2009 - 17:08:00 EST


On Wed, 22 Apr 2009, Steven Whitehouse wrote:

> I'd like to add a new bitop, __ffs64() which I need in order to fix a
> bug in GFS2. The question is, where should it go?

I think the location is right.

> On 64 bit arches, __ffs64() would be a synonym for __ffs(), but on 32
> bit arches it degenerates to a conditional plus a call to __ffs(). I'm
> assuming that there would not be a lot of point in optimising this
> operation on 32 bit arches even if such an instruction was available, so
> that I should do something like the below patch.
>
> Does that seem reasonable, or should I give it a separate header file
> under asm-generic/bitops/ like some of the similar operations? It looks
> like I'd have to touch a lot of other files if I were to go that route,

One issue may be that some 32 bit architectures have a better way of doing
64 bit ffs.

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