linux-kernel - Re: [PATCH] tcp_cubic: use 32 bit math

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Message-ID: <45EF7EB7.8040806@linux-foundation.org>
Date:	Wed, 07 Mar 2007 19:10:47 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
CC:	w@....eu, rkuhn@....physik.tu-muenchen.de, andi@...stfloor.org,
	dada1@...mosbay.com, jengelh@...ux01.gwdg.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_cubic: use 32 bit math

David Miller wrote:
> From: Stephen Hemminger <shemminger@...ux-foundation.org>
> 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 <shemminger@...ux-foundation.org>
>>     
>
> 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;

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