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    SubjectALIGN via ilog2 without gccisms (Re: [PATCH] Fix get_order())
    > From: David Howells
    > Newsgroups: gmane.linux.kernel
    > Subject: Re: [PATCH] Fix get_order()
    > Date: Wed, 07 Mar 2007 11:43:06 +0000
    > Various archs (including i386, x86_64, powerpc and frv) have instructions that
    > can be used to calculate integer log2(N).
    Probably it can be used to get rid of gccisms and "type fluff" due to
    bitwise arithmetics in ALIGN?

    #define ALIGN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1)
    #define __ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))

    like that:

    #define ALIGN(x,y) __ALIGN_MASK(x,ilog2(y))
    #define __ALIGN_MASK(x,bits) (((((x) >> (bits)) << 1) + 2) << (bits - 1))

    Note side effect, that this one always yields even result. Maybe this is
    good, due to avoidance of misaligned access.

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      Last update: 2007-03-07 16:57    [W:0.020 / U:7.816 seconds]
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