Re: [Xen-devel] [PATCH v3 07/13] x86: Add functions for 64-bit integer arithmetic

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/04/2016 08:15 PM, Haozhong Zhang wrote:
> On 01/04/16 13:26, Boris Ostrovsky wrote:
> > On 12/30/2015 10:03 PM, Haozhong Zhang wrote:
> > > This patch adds several functions to take multiplication, division and
> > > shifting involving 64-bit integers. Those functions are derived from
> > > Linux kernel and will be used by later patches to calculate scaling
> > > ratio and scaled TSC.
> > >
> > > Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> >
> > (although I not sure why you decided to change Linux' code in mul64() below)
> >
> >
> >
> > > +    c = (u64)rl.l.high + rm.l.low + rn.l.low;
> > > +    rl.l.high = c;
> > > +    c >>= 32;
> > > +    c = c + rm.l.high + rn.l.high + rh.l.low;
> > > +    rh.l.low = c;
> > > +    rh.l.high += (u32)(c >> 32);
> I took these code from my KVM patches, but it seemed it was refactored
> later and also inlined with mul_u64_u64_shr(). However, above code is
> still equivalent to the current Linux code (if we take mul64() from
> mul_u64_u64_shr() in Linux), so I think it should be fine. Or do you
> want me to make them consistent with Linux code?
Yes, it is equivalent to what's in Linux. I don't think you need to do 
anything, I was just curious why the two routines look slightly different.

-boris

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