netdev - Re: [RFC] div64

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Message-ID: <20070226160708.3c7a8d29@freekitty>
Date:	Mon, 26 Feb 2007 16:07:08 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC] div64_64 support

On Tue, 27 Feb 2007 01:05:26 +0100 (MET)
Jan Engelhardt <jengelh@...ux01.gwdg.de> wrote:

> 
> On Feb 26 2007 15:44, Stephen Hemminger wrote:
> >> >-		x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3;
> >> >+		x = (2 * x + (u32) (a / x*x)) / 3;
> >> 
> >> Previously there was div64_64(a, x*x) which is equivalent to
> >> (a)/(x*x), or just: a/(x^2). But now you do a/x*x, which is
> >> equivalent to a*x/x (in the domain of real numbers). Furthermore,
> >> a/x*x is a-(a%x), which does not even remotely match a/(x^2).
> >> 
> >Been there, done that, don't want to repeat it...
> 
> I am sorry I don't quite follow.

Once before a missed paren's caused a TCP congestion window bug that
took 6 months before it was found...

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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