linux-kernel - Re: [PATCH] trivial, document that div64_u64() is not precise on 32bit platforms

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Message-ID: <1280880761.10330.5.camel@snog.zork.net>
Date:	Tue, 03 Aug 2010 19:12:41 -0500
From:	Ben Woodard <woodard@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"Behlendorf, Brian D." <behlendorf1@...l.gov>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Mark Grondona <mgrondona@...l.gov>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] trivial, document that div64_u64() is not precise on
 32bit platforms

Andrew,

On Tue, 2010-08-03 at 15:28 -0700, Andrew Morton wrote:
> Well that was a bit lazy of us - I wonder how hard it is to fix.
> 
> At present people will test their code on 64-bit only to find out
> later
> that it doesn't work correctly on 32-bit.  Bad.  Perhaps we should
> similarly break the 64-bit version :)

I just talked to Brian. He's got an implementation that does the
division correctly. He's going to clean it up and send you a patch so
that it will work without losing precision on both 32b and 64b. It is
based upon public domain code from  http://www.hackersdelight.org and
has been proven to be correct in all cases.

-ben


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