Subject: Re: [PATCH] tcp_cubic: use 32 bit math

From: Willy Tarreau <[email-masked]>
Date: Thu, 8 Mar 2007 05:16:28 +0100

On Wed, Mar 07, 2007 at 07:10:47PM -0800, Stephen Hemminger wrote:
> David Miller wrote:
> >From: Stephen Hemminger <[email-masked]>
> >Date: Wed, 7 Mar 2007 17:07:31 -0800
> >
> >  
> >>The basic calculation has to be done in 32 bits to avoid
> >>doing 64 bit divide by 3. The value x is only 22bits max
> >>so only need full 64 bits only for x^2.
> >>
> >>Signed-off-by: Stephen Hemminger <[email-masked]>
> >>    
> >
> >Applied, thanks Stephen.
> >
> >What about Willy Tarreau's supposedly even faster variant?
> >Or does this incorporate that set of improvements?
> >  
> That's what this is:
>    x = (2 * x + (uint32_t)div64_64(a, (uint64_t)x*(uint64_t)x)) / 3;

Confirmed, it's the same. BTW, has someone tested on a 64bit system if
it brings any difference ?

Willy