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    SubjectRE: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2

    > -----Original Message-----
    > From: George Anzinger []
    > Pallipadi, Venkatesh wrote:
    > >
    > >
    > >>-----Original Message-----
    > >>From: Andrew Morton []
    > >>
    > >>We seem to keep on proliferating home-grown x86 64-bit math
    > functions.
    > >>
    > >>Do you really need these? Is it possible to use do_div() and
    > >>the C 64x64
    > >>`*' operator instead?
    > >>
    > >
    > >
    > >
    > > We can change these handcoded 64 bit divs to do_div, with just an
    > > additional data copy
    > We already have this in .../include/asm-i386/div64.h. Check usage in
    > .../posix-timers.c to cover archs that have not yet included it in
    > there div64.h.

    Yes. We can surely use div_long_long_rem from div64 in place of defining
    this again. This kind of code is already there in the existing ia32 timer
    code too. I will try and come up with a cleanup patch to replace all
    these individual asm div statements.

    > > (as do_div changes dividend in place). But, changing mul
    > into 64x64 '*'
    > > may be tricky.
    > > Gcc seem to generate a combination of mul, 2imul and add,
    > where as we
    > > are happy with
    > > using only one mull here.
    > You just need to do the right casting. It should like
    > u64=u32*(u64)u32 as in .../kernel/posix-timers.c. This
    > could also be
    > signed with the same results. If you really need to do a u64*u32, it
    > will do that as well but takes two mpys. In this case you will need
    > to do it unsigned to eliminate the third mpy.

    Interesting. Is this casting to generate proper mul instruction
    some sort of C standard or is it a gcc feature. I just want to
    make sure doing this way won't break on some other compiler
    (or on some other version of gcc itself).

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