lkml.org 
[lkml]   [2007]   [Jun]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Add "is_power_of_2" checking to log2.h.
    Robert P. J. Day wrote:
    >
    > seriously, though, there is the potential of breaking something with
    > this change since you can see how there is some inconsistency in how
    > it's done *now* just for powerpc which, in some places, defines its
    > own versions of this:
    >
    > ./arch/ppc/mm/pgtable.c:
    > #define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
    > ./arch/ppc/syslib/ppc85xx_rio.c:
    > #define is_power_of_2(x) (((x) & ((x) - 1)) == 0)
    > ./arch/powerpc/mm/pgtable_32.c:
    > #define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
    >
    > note how the first and third macros *won't* consider zero a power of
    > two, while the second one *will*. hence the need for a single
    > standard for all of this, just to play it safe.
    >

    I suspect the reason the test for zero was omitted is because the author
    didn't want the extra cost (the test for zero needs an extra branch on a
    lot of architectures.)

    -hpa
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-06-12 01:17    [W:0.020 / U:31.544 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site