Re: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take2

[George Anzinger]

Pallipadi, Venkatesh wrote:
> > -----Original Message-----
> > From: Andrew Morton [mailto:akpm@xxxxxxxx] 
> >
> > 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.

> (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.
>

--
George Anzinger   george@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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