linux-kernel - Re: [RFC] div64

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Message-Id: <84C47260-4B57-4568-8197-58F438A6F737@e18.physik.tu-muenchen.de>
Date:	Tue, 6 Mar 2007 16:10:08 +0100
From:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC] div64_64 support

Hi Andi!

On 6 Mar 2007, at 15:45, Andi Kleen wrote:

>> <rant>
>> Let me see... You throw code like that and expect someone to actually
>> understand it in one year, and be able to correct a bug ?
>
> To be honest I don't expect any bugs in this function.
>
>> </rant>
>>
>> Please add something, an URL or even better a nice explanation,  
>> per favor...
>
> It's straight out of Hacker's delight which is referenced in the  
> commit
> log.
>
And it's pretty neat, too. Hint: (y+1)**3 = y**3 + 3*y**2 + 3*y + 1.  
The algorithm is exactly the same as for calculating the cubic root  
on paper, digit by digit. I found that algo in the school notebook of  
my grandpa (late 1920ies), a pity that it's not taught anymore...  
pocket calculators _do_ have downsides ;-)

Ciao,
                     Roland

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