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    SubjectRe: [RFC] __ffs64()
    On Apr. 23, 2009, 11:22 +0300, Steven Whitehouse <swhiteho@redhat.com> wrote:
    > Hi,
    >
    > On Wed, 2009-04-22 at 16:59 -0400, Christoph Lameter wrote:
    >> 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.
    >>
    > Yes, thats what I was worried about. I don't have a wide enough
    > knowledge of the different architectures to make a judgement about
    > whether this is likely or not.
    >
    > I guess maybe the right thing to do is to leave it as I did it in the
    > patch and if an arch wants to create its own implementation, then it
    > could be moved at that stage.

    Agreed.

    Benny

    >
    > Steve.
    >
    >
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